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CALSCALE:GREGORIAN
METHOD:PUBLISH
X-WR-CALNAME:Theory of Condensed Matter: Hard Condensed Matter
X-WR-TIMEZONE:Europe/Berlin
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Prof Dmitry Bud
ker on THE PERFECT (NV) DEFECT: MAKING SENS(OR) OF DIAMOND
DTSTART;VALUE=DATE-TIME:20140528T150000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2937@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:I will provide a general and accessible introduction to the ni
trogen-vacancy color centers in diamond\, explain why these have been a fo
cus of intense research in recent years\, and will also describe several a
pplications and the direction our group and various collaborators have bee
n pursuing at Berkeley\, Mainz\, in the desert of Negev\, and elsewhere.
LOCATION:Lorentz-Room\, 05-127\, Staudingerweg 7
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2937
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Prof. Dr. H. C.
Schneider on Demagnetization dynamics and spin-dependent lifetimes in fer
romagnets
DTSTART;VALUE=DATE-TIME:20140617T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2938@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:I will present some theoretical results on spin-dependent carr
ier dynamics/magnetizatin dynamics in ferromagnets after excitation by ult
rashort optical pulses. \n\nUltrafast demagnetization has been well establ
ished experimentally for more than 10 years\, but there is still no agreem
ent on the microscopic mechanism behind it. I will give a brief review of
the experimental facts and the different theoretical approaches\, and then
focus on the contribution of Elliott-Yafet spin-flip scattering. Although
this concept from semiconductor physics has long been the most promising
candidate to explain ultrafast demagnetization\, there have always been pr
oblems with it and its importance has recently been challenged.[1]\n\nWe h
ave done the first dynamical calculations of Elliott-Yafet scatterin in fe
rromagnets based on an ab-initio description of the optical exciation and
electron-phonon scattering. [2] Recently\, we have also included a time-de
pendent exchange splitting in the dynamics [3]. Our results indicate that
Elliott-Yafet type spin-flip scattering does play an important role in the
demagnetization dynamics of ferromagnets\, but only if it is "amplified"
by a time-dependent exchange splitting.\n\nI will also briefly present our
recent ab-initio based calculation of spin-dependent lifetimes in ferroma
gnets including spin-orbit coupling\n[4]\, which agrees\, for the first ti
me\, with 2-photon photoemission data. These results cast some doubt on th
e importance of superdiffusive spin transport\, which has\, so far\, been
based on computed spin-dependent lifetimes that are in contradiction with
experiments.\n\n\n[1] See\, e.g.\, Eschenlohr et al.\, Nature Materials 12
\, 332 (2013)\, Battiato et al.\, Phys. Rev. B 86\, 024404 (2012)\n[2] Ess
ert & Schneider\, Phys. Rev. B 84\, 224405 (2011)\, J. Appl. Phys. 111\,
07C514 (2012).\n[3] Mueller et al.\, Phys. Rev. Lett. 111\, 167204 (2013).
\n[4] Kaltenborn & Schneider\, arXiv:1403.4728 (2014).
LOCATION:Seminar Room K\, Building 2/413
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2938
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Prof. Dr. Ronny
Thomale on Entanglement spectrum of Fractional Quantum Hall states and Qu
antum spin chains
DTSTART;VALUE=DATE-TIME:20140701T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2940@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We give a complete definition of the entanglement gap separati
ng low-energy\, topological levels\, from high-energy\, generic ones\, in
the "entanglement spectrum" of Fractional Quantum Hall (FQH) states and qu
antum spin chains. By removing the magnetic length inherent in the FQH pro
blem - a procedure which we call taking the "conformal limit"\, we find th
at the entanglement spectrum of an incompressible ground state of a generi
c (i.e. Coulomb) lowest Landau Level Hamiltonian re-arranges into a low-(e
ntanglement) energy part separated by a full gap from the high energy enta
nglement levels. As previously observed\, the counting of these levels sta
rts off as the counting of modes of the edge theory of the FQH state\, but
quickly develops finite-size effects which we show can also serve as a fi
ngerprint of the FQH state. As the sphere manifold where the FQH resides g
rows\, the level spacing of the states at the same angular momentum goes t
o zero\, suggestive of the presence of relativistic gapless edge-states. B
y using the adiabatic continuity of the low entanglement energy levels\, w
e investigate whether two states are topologically connected. For the spin
chains\, the entanglement spectrum from a cut in momentum space allows to
study the dimerization transition\, bulk excitation state counting\, and
the manifestation of logarithmic CFT correction purely from the ground sta
te wave function.\nIt provides a new formulation of non-local order in qua
ntum spin chains.
LOCATION:Seminarraum k\, Bau 2/413
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2940
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: J.-Prof Dr. Mat
teo Rizzi on Optimal persistent currents for interacting bosons on a 1D ri
ng with a gauge field
DTSTART;VALUE=DATE-TIME:20140527T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2944@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We study persistent currents for interacting one-dimensional (
1D) bosons on a tight ring trap\, subjected to a rotating barrier potentia
l\, which induces an artificial \\(U(1)\\) gauge field.\nWe show that\, at
intermediate interactions\, the persistent current response is maximal\,
due to a subtle interplay of effects due to the barrier\, the interaction
and quantum fluctuations.\nThese results are relevant for ongoing experime
nts with ultracold atomic gases on mesoscopic rings.
LOCATION:Seminar Room K\, Building 2/413
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2944
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Elio König on
Disordered surfaces of 3D topological insulators: interactions and/or stro
ng magnetic field
DTSTART;VALUE=DATE-TIME:20140702T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2950@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The fate of the Dirac-like surface states of 3D topological in
sulators (TIs) under the influence of electron-electron interactions and/o
r a strong magnetic field is investigated.\n\nFirst\, a theory of combined
interference and interaction effects on the diffusive transport propertie
s of 3D topological insulator surface states is presented. We focus on a s
lab geometry (characteristic for most experiments) and show that intersurf
ace interaction between the two major surfaces is relevant in the renormal
ization group (RG) sense and the case of decoupled surfaces is therefore u
nstable.\nWe predict a characteristic non-monotonic temperature dependence
of the conductivity. In the infrared (low-temperature) limit\, the system
flows into a metallic fixed point. At this point\, even initially differe
nt surfaces have the same transport properties.\n\nSecond\, the unconventi
onal (half-integer) quantum Hall effect for a single Dirac fermion is anal
yzed. The following important questions\, which were not or only partially
answered to present date\, are discussed:\n\n(i) How can half-integer Hal
l conductance g_{xy} be measured experimentally? (ii) Doesn¹t Laughlin¹s
flux insertion argument forbid half-integer g_{xy}? (iii) What is the fie
ld theory describing the localization physics of the single Dirac fermion
quantum Hall effect?\n\nThe RG flow and the resulting phase diagram are ex
amined. Starting values of the RG flow are given by the semiclassical cond
uctivity tensor which is obtained from the Boltzmann transport theory of t
he anomalous Hall effect.\n\n\nReferences:\n\nE. J. König\, P. M. Ostrovs
ky\, I. V. Protopopov\, I. V. Gornyi\, I. S.\nBurmistrov\, A. D. Mirlin\,
PRB 88\, 3\, pp. 035106 (2013).\n\nE. J. König\, P. M. Ostrovsky\, I. V.
Protopopov\, I. V. Gornyi\, I. S.\nBurmistrov\, A. D. Mirlin\, arXiv:1406
.5008 (2014).
LOCATION:Medienraum (03-431)\, Staudinger Weg 7
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2950
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Björn Sbierski
on Disordered Weyl Semimetals
DTSTART;VALUE=DATE-TIME:20140725T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2951@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Weyl semimetals are paradigmatic topological gapless phases in
three dimensions. After a general introduction\, we discuss the effect of
disorder on charge transport in Weyl semimetals. For a single Weyl node w
ith energy at the degeneracy point and without interactions\, theory predi
cts the existence of a critical disorder strength beyond which the density
of states takes on a nonzero value. Predictions for the conductivity are
divergent\, however. We present a numerical study of transport properties
for a disordered Weyl cone at zero energy. For weak disorder our results a
re consistent with a renormalization group flow towards an attractive pseu
doballistic fixed point with zero conductivity and a scale-independent con
ductance\; for stronger disorder diffusive behavior is reached. We identif
y the Fano factor as a signature that discriminates between these two regi
mes.
LOCATION:Seminar room K
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2951
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Charles Gould o
n Transport investigations on a magnetic topological insulator – A work
in progress
DTSTART;VALUE=DATE-TIME:20140709T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2952@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The reports on observing the quantum anomalous Hall effect (AH
E) in Cr-doped (Bi\,Sb)2Te3 has focused significant interest onto this mat
erial system for its potential as a magnetic topological insulator. In thi
s talk I will report on our on-going efforts in growing and characterizing
of this material system. \nIn particular\, I will discuss several experim
ental issues which make this material challenging to work with in transpor
t studies\, and show how these must be treated with extreme care in order
to get reliable transport results. While we do not observe any quantizatio
n of the effect in our samples\, a strong AHE is nevertheless seen\, which
combined with SQUID investigations can be used to extract information abo
ut the nature of the magnetic states in our layers.\nOur observations are
consistent with that of a magnetically viscous magnetic state\, which tend
s to stabilize into a true ferromagnetic state in thick layers\, but take
on more of a superparamagnetic character in the thin films we use in the t
ransport studies. Whether such a state is representative of a homogenous l
ayer\, or results from inhomogeneity in the distribution and/or phase of t
he included Cr atoms is a topic of on-going investigations.
LOCATION:Seminar Room K\, Staudinger Weg 9
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2952
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Alex Levchenko
on Kinetics of 1d electrons beyond the Luttinger liquid paradigm
DTSTART;VALUE=DATE-TIME:20140729T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:2966@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We will discuss violation of spin-charge separation in generic
nonlinear Luttinger liquids and investigate its effect on the relaxation\
, thermal and electrical transport of genuine spin-1/2 electron liquids in
ballistic quantum wires. We identify basic scattering processes compatibl
e with the symmetry of the problem and conservation laws that lead to the
decay of plasmons into the spin modes and also describe their backscatteri
ng. We derive a closed set of coupled kinetic equations for the spin-charg
e excitations and solve the problem of electrical and thermal conductance
of interacting electrons for an arbitrary relation between the quantum wir
e length and spin-charge equilibration length.
LOCATION:Seminar room K
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/2966
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Prof. Dr. Vital
ii Dugaev on Edge scattering of electrons in graphene
DTSTART;VALUE=DATE-TIME:20141111T141500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3056@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The contribution of edge scattering to the conductance of grap
hene nanoribbons and nanoflakes is discussed. We used the Boltzmann equati
on approach with the specific boundary conditions for the distribution fun
ction at the edges\, which take into account different character of the el
ectron scattering from edge imperfections\, depending on the incoming angl
e of electron. Using the solution of kinetic equation and various possible
types of the boundary conditions for the electron wave function at the ed
ge of graphene\, we found the dependence of the momentum relaxation time a
nd conductance on the geometric sizes and on the carrier density. We also
consider the case of ballistic nanoribbon and nanodisk\, for which the edg
e scattering is the main mechanism of momentum relaxation.
LOCATION:Galilei room
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3056
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Dr. Salvatore M
anmana on Far from equilibrium quantum magnetism with ultracold polar mole
cules
DTSTART;VALUE=DATE-TIME:20141118T141500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3071@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Recent theoretical progress has indicated how to emulate tunea
ble models of quantum magnetism with ultracold polar molecules. In this ta
lk\, I am going to discuss the underlying ideas and the effective model ob
tained from this ansatz\, which is a generalised t-J model with long-range
interactions. The simplest realization in 1D is a t-J_perp model\, in whi
ch only interactions of the XY-type survive. Using the DMRG\, I discuss th
e effect of the absence of the original SU(2) symmetry of the t-J-model on
the phase diagram\, in particular in superconducting phases. In the secon
d part of my talk\, I will discuss features of these quantum simulators wh
en going out-of-equilibrium.
LOCATION:Galilei-Room\, Bau 2/413\, 01-128
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3071
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Yuta Yamane on
Effective forces in ferromagnets -spinmotive force\, anomalous Hall effect
\, and domain wall resistance
DTSTART;VALUE=DATE-TIME:20141125T141500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3082@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In ferromagnetic metals\, the strong exchange coupling of the
conduction electron with the local magnetization allows us to adopt an adi
abatic approximation\, in which the subspaces for the majority and minorit
y electrons become independent but with a gauge field coming into a play.\
nThe gauge field is spin-dependent and known to cause nontrivial electromo
tive force and anomalous Hall effect. In this talk\, by taking into accoun
t the non-adiabatic spin dynamics and the spin-orbit coupling\, we will se
e that there can appear an additional electromotive force and domain wall
resistances.\nJGU Mainz
LOCATION:Galilei room\, Staudinger Weg 9\, 01-128\, 1st floor
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3082
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Ora Entin-Wohlm
ann on “Thermoelectricity in nano-junctions”
DTSTART;VALUE=DATE-TIME:20150205T110000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3121@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Following a general introduction into thermoelectricity in coh
erent electronic junctions\, the efficiencies/coefficients of performance
of three-terminal devices\, comprising two electronic terminals and a ther
mal one (e.g.\, a boson bath) will be discussed. In particular\, two proce
dures are analyzed. (a) One of the electronic terminals is cooled by inves
ting thermal power (from the thermal bath) and electric power (from voltag
e applied across the electronic junction)\; (b) The invested thermal power
from the boson bath is exploited to cool one electronic terminal and to p
roduce electric power. Rather surprisingly\, the coefficient of performanc
e of (b) can be enhanced as compared to that of (a).
LOCATION:Medienraum 03-431
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3121
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Sebastian Müll
er on "Spin accumulation and diffusion in magnetic Multilayers"
DTSTART;VALUE=DATE-TIME:20150206T090000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3122@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:"In this talk I will discuss the effect of the spin memory los
s on interfaces of ferromagnetic (F) and non-magnetic (N) materials in th
e stackings N|F and N|F|N. \nIn particular\, results on the size of spin f
lip and spin accumulation gaps at the interfaces will be presented.\nThe t
heoretical description is based on a limit of the theory of perpendicular
magneto-resistance in magnetic multilayers by Valet and Fert.”
LOCATION:Galileiraum\, 01-128\, Staudinger Weg 9
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3122
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Prof. Amnon Aha
roni on Spin Filtering: how to write and read quantum Information on mobil
e qubits
DTSTART;VALUE=DATE-TIME:20150206T103000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3123@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Quantum computing requires the ability to write and read quant
um information on the spinors of electrons. This work considers mobile ele
ctrons\, which move through mesoscopic (or molecular) quantum networks (ma
de of quantum wires or of arrays of quantum dots). Combining spin-orbit in
teractions\, whose strength can be tuned by external gate voltages\, and t
he Aharonov-Bohm flux\, which can be tuned by an external magnetic field\,
one can manipulate the properties of such networks\, so that the outgoing
electrons are polarized along a desired direction. This amounts to 'writi
ng' the desired information on the spinor of the electrons. Given a beam o
f polarized electrons\, the charge conductance of the same network depends
on their polarization\, allowing 'reading' the qubit information. Specif
ic results will be presented for a simple closed interferometer. [1] The t
alk will also report on more recent work:\n(a) The above filtering is robu
st against leaking of electrons\, in an open interferometer. [2] (b) Filte
ring can also be achieved for a single one dimensional chain which has spi
n-orbit interactions\, when the chain vibrates in the transverse direction
. [3] (c) Real time evolution of the polarizations in the filter. [4]\n\n
[1] A. Aharony\, Y. Tokura\, G. Z. Cohen\, O. Entin-Wohlman\, and S. Katsu
moto\, Filtering and analyzing mobile qubit information via Rashba-Dressel
haus- Aharonov-Bohm interferometers Phys. Rev. B 84\, 035323 (2011)\;(arXi
v:1103.2232)\n\n[2] S. Matityahu\, A. Aharony\, O. Entin-Wohlman and S. Ka
tsumoto\, Robustness of spin filtering against current leakage in a Rashba
-Dresselhaus-Aharonov-Bohm interferometer Phys. Rev. B 87\, 205438 (2013)\
; (arXiv:1302.6772)\n\n[3] R. I. Shekhter\, O. Entin-Wohlman\, and A. Ahar
ony Mechanically-controlled Rashba spin-splitters Phys. Rev. Lett. 111\,
176602 (2013)\; (arXiv:1306.5125)\n\n[4] M. Wei-Yuan Tu\, A. Aharony\,W-M
Zhang and O. Entin-Wohlman Real-time dynamics of spin-dependent transpor
t through a double-quantum-dot Aharonov-Bohm interferometer with spin-orbi
t interaction.\nPhys. Rev. B 90\, 165422 (2014)\; (arXiv:1406.6258)
LOCATION:Galileiraum\, 01-128\, Staudinger Weg 9
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3123
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Binghai Yan on
Quantum Anomalous Hall Effects on the Novel Honeycomb Material Stanene
DTSTART;VALUE=DATE-TIME:20150211T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3125@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Recently\, the long-sough quantum anomalous Hall effect was re
alized in a magnetic topological insulator. However\, the requirement of a
n extremely low temperature (approximately 30 mK) hinders realistic applic
ations. Based on ab initio band structure calculations\, we propose a quan
tum anomalous Hall platform with a large energy gap of 0.34 eV on honeycom
b lattices comprised of Sn\, called stanene. The ferromagnetic (FM) order
forms in one sublattice of the honeycomb structure by controlling the surf
ace functionalization rather than dilute magnetic doping\, which is expect
ed to be visualized by spin polarized STM in experiment. Strong coupling b
etween the inherent quantum spin Hall state and ferromagnetism results in
considerable exchange splitting and\, consequently\, an FM insulator with
a large energy gap. The estimated mean-field Curie temperature is 243 K. T
he large energy gap and high Curie temperature indicate the feasibility of
the quantum anomalous Hall effect in the near-room-temperature regions.\n
\nRefs. PRL 113\, 256401 (2014)\; PRL 111\, 136804 (2013).
LOCATION:Gernot Graeff-Raum\, Staudinger Weg 7\, room 05-431
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3125
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Thierry Valet o
n Selected topics in spintronics
DTSTART;VALUE=DATE-TIME:20150212T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3129@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Thierry Valet will provide an overview of his current research
interests in spintronics\, both in the area of spin transport theory (out
of equilibrium quantum field theory of transverse spin transport in "meta
ls") and micro-magnetic theory (spectral formulation of linear and weakly
non linear spin transfer induced dynamics).
LOCATION:MITP\, Raum 02-439\, Staudinger Weg 9
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3129
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Yuriy Mokrousov
on Topologocial Spintronics: an ab-initio perspective
DTSTART;VALUE=DATE-TIME:20150331T141500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3164@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Lorentz Room ( Staudingerweg 9\, 01-127)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3164
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Casper Drukier
on "Non-analytic corrections in Fermi liquids and multi-channel scattering
"
DTSTART;VALUE=DATE-TIME:20150602T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3227@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Landau's Fermi liquid theory has been the main tool for invest
igating interactions in condensed matter systems at low energies for sever
al decades. It describes the excitations of the interacting system through
long-lived quasi-particles which have the same\, albeit renormalized\, pr
operties as the excitations of the non-interacting system. As such it woul
d be natural to expect that various quantities such as the susceptibility
and heat capacity follow analytic series in temperature or external magnet
ic field. Recently\, however\, situations where this does not remain true
have attracted much attention. In this talk I will discuss these non-analy
ticities\, which appear due to effective long-range interactions between t
he quasi-particles\, and show that they also appear in quasi-particle prop
erties such as the Lande g-factor\, and in experimentally accessible quant
ities such as the conductivity and tunnelling density of states. I will al
so show that they are determined fully by low-energy scattering processes
and discuss how to classify these. Finally I will discuss a new approach\,
based on the functional renormalization group\, to deal with systems wher
e scattering is dominated by processes in multiple scattering channels. As
an illustration of the method I will consider the so-called X-ray problem
.\n\n[1] C. Drukier\, P. Lange\, and P. Kopietz\, Eur. Phys. J. B 88\, 41
(2015)\n[2] P. Lange\, C. Drukier\, A. Sharma\, and P. Kopietz\, ArXiv:150
2.06625
LOCATION:Galilei Room
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3227
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Joo-Von Kim on
Magnetization dynamics in chiral spin textures: Spin wave channelling and
skyrmion oscillations
DTSTART;VALUE=DATE-TIME:20150721T141500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3245@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Chiral symmetry can be broken in magnetic thin films and multi
layers\, leading to the appearance of an anisotropic exchange interaction
of the Dzyaloshinskii-Moriya (DM) form. We have studied theoretically how
the DM interaction can strongly modify measurable features of spin wave ex
citations in ultrathin films with perpendicular magnetic anisotropy. We wi
ll show how nonreciprocal channelling can appear in systems with domain wa
lls\, which has consequences for spin wave modes in confined geometries\,
such as strips and dots. We will also describe the breathing dynamics and
current-driven oscillations of isolated skyrmions in ultrathin film dots.
LOCATION:Galilei Room
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3245
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Roberto Raimond
i on Spin current swapping and spin Hall effect in a 2DEG
DTSTART;VALUE=DATE-TIME:20160126T141500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3385@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In this talk I will present some of the results obtained over
the last year about spin-orbit induced effects in a two-dimensional electr
on gas. At first I will discuss the spin current swapping effect according
to which a spin current flowing in the i direction with spin polarization
along the j axis is converted into a spin current flowing in the j direct
ion with spin polarization along the i axis. \nI will analyze the circumst
ances under which to observe the effect and its connection with the spin H
all effect. As a second topic I will focus on the spin Hall effect due to
the skew-scattering mechanism induced by phonon scattering. A comparison
will be made with the standard skew-scattering due to impurities and the
consequences for the temperature dependence of the spin Hall angle will be
analyzed. Finally\, I will present a model with a striped Rashba spin-orb
it coupling\, which could possibly be realized in LAO/STO interfaces. Such
a non homogeneous spin-orbit coupling may give rise to a spin Hall effect
robust with respect to impurity scattering.
LOCATION:Galileiraum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3385
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Cosimo Gorini o
n Thermoelectric conversion in disordered nanowires
DTSTART;VALUE=DATE-TIME:20160128T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3386@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Semiconductors have been employed for decades as the thermoele
ctric materials of choice. More recently\, gated semiconductor nanowires h
ave shown remarkable thermoelectric properties\, well beyond those of stan
dard bulk devices\, and are under intense experimental investigation. Inde
ed\, nanostructuration allows -- at least in principle -- to engineer syst
ems capable of meeting the somewhat contradictory requirements of an ideal
thermoelectric device: (i) to be a good charge and a poor thermal conduct
or (ii) exhibiting strong particle-hole asymmetry\, (iii) which works up t
o room temperature and (iv) is based on non-polluting and abundant materia
ls.\nI will show that strongly disordered nanowires\, where conduction tak
es place via phonon-assisted (Mott) hopping between localised states\, act
indeed as very promising thermoelectrics. In particular\, I will discuss
impurity band-edge transport and an asymmetric 3-terminal setup as two com
plementary approaches to realising flexible and performant (non-local) the
rmoelectric devices.
LOCATION:Medienraum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3386
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Kyoung-Whan Kim
on CANCELLED
DTSTART;VALUE=DATE-TIME:20160126T150500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3387@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galileiraum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3387
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Kyoung-Whan Kim
on Spin transport related to spin-orbit coupling
DTSTART;VALUE=DATE-TIME:20160128T150500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3395@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetism is a promising candidate as the basis of next genera
tion electronic devices. Electrical manipulation of magnetization would al
low it to be controlled rapidly in spite of its non-volatile nature. As pe
ople pursue smaller and smaller sized devices\, the effects of broken symm
etries become more and more important. In particular\, strong interface sp
in-orbit coupling as a consequence of inversion symmetry breaking shows a
number of interesting features. In this talk\, I present two topics relate
d to spin-orbit coupling. First\, despite its importance\, our understandi
ng of spinorbit coupling is still incomplete. In this work\, we generalize
an existing model for electron spin transport near interfaces to construc
t an analytic theory for interface spin-orbit coupling that can be applied
to various systems\, such as magnetic bilayers\, topological insulators\,
and ferromagnetic insulators. The theory gives not only corrections to th
e existing theory\, but also qualitatively different physics. Second\, we
demonstrate that the understanding of spin-orbit coupling effects in magne
tic systems is also helpful for other systems. By utilizing a one-toone co
rrespondence between textured magnetic systems and a spin-orbit coupling s
ystems\, we demonstrate the existence of an overlooked contribution to tex
tured magnetic systems\, which one can infer from knowledge of spin-orbit
coupling effects. These two topics indicate that theoretical study of spin
-orbit coupling in magnetic systems not only advances applications of spin
tronics in devices but also deepens our understanding of magnetic systems.
LOCATION:Medienraum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3395
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Peter Kopietz o
n Rayleigh-Jeans condensation of pumped magnons in thin film ferromagnets
DTSTART;VALUE=DATE-TIME:20160216T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3396@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We show that the formation of a magnon condensate in thin ferr
omagnetic films can be explained within the framework of a classical stoch
astic nonMarkovian Landau-Lifshitz-Gilbert equation where the properties o
f the random magnetic field and the dissipation are determined by the unde
rlying phonon dynamics. We have numerically solved this equation for a tan
gentially magnetized yttrium-iron garnet film in the presence of a paralle
l parametric pumping field. We obtain a complete description of all stages
the nonequilibrium time evolution of the magnon gas which is in excellent
agreement with experiments. Our calculation proves that the experimentall
y observed condensation of magnons in yttrium-iron garnet at room temperat
ure is a purely classical phenomenon which should be called Rayleigh-Jeans
rather than Bose-Einstein condensation.
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3396
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Xavier Waintal
on Ultrafast pulses\, spin torque and artificial antiferromagnets
DTSTART;VALUE=DATE-TIME:20160204T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3401@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Artificial antiferromagnets (Ferromagnetic-Normal-Ferromagneti
c spin valves (antiferromagnetically coupled by the interlayer exchange in
teraction) can be viewed as the spintronics version of the Fabry-Perot int
erferometer. In this talk\, I will introduce the concept of dynamical cont
rol of interference pattern with ultra-fast voltage pulses. I will show th
at this idea can be used on artificial antiferromagnets to control the mag
netic exchange interaction leading to a new sort of (dynamical) spin torqu
e. In a second part\, I will discuss the magnetic response of these artifi
cial antiferromagnets to spin torque\, that naturally leads to spin torque
oscillator (STO) behavior even in the absence of external fields. I will
also take this opportunity to advertise our open source quantum transport
code Kwant (http://kwant-project.org)\, that was used to obtain a large fr
action of the results shown in this talk.
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3401
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Stanislav Chado
v on Constructive Aspects of Disorder in Solids
DTSTART;VALUE=DATE-TIME:20160407T110000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3456@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Most of the material science problems can be reduced to a rath
er generic formulation: how to increase an intensity of the useful propert
ies or how to get rid of the unwanted ones. Diversity of the degrees of fr
eedom in complex systems makes such “signal-to-noise” control rather s
ophisticated and expensive. Within the state-of-the-art nano-scale applica
tions the quality requirements for the basic technological elements are of
ten stringent: high crystalline order\, precision of target compositions\,
chemical or mechanical compatibility between different materials\, precis
e number of atomic layers\, etc. Once these requirements appear to be too
resource-demanding\, one might think about the alternatives provided by di
sorder. In this context\, certain improvement can be achieved by introduci
ng a specific type of disorder\, suppressing the “noise” intensity\, b
ut retaining the “signal”. On the nano-scale\, such engineering requir
es the established relationships between the properties\, electronic struc
ture\, and a particular type of disorder. Here I would like to discuss the
modelling of certain constructive aspects\, based on the ab-initio techni
ques dealing with disorder explicitly (Coherent Potential Approximation an
d its recent extensions). In particular\, I will focus on the example of t
he alternative half-metallicity induced by the spin-selective electron loc
alization tuned by the chemical disorder within the class of Heusler mater
ials.\n
LOCATION:Medienraum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3456
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Michael Fechner
on Parity odd magnetism in transition metal oxides and the pseudo-gap pha
se in cuprate superconductors
DTSTART;VALUE=DATE-TIME:20160413T103000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3476@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:A characteristic of ferroic materials is the emergence of a te
mporally static finite expectation value of an order parameter. Here\, we
introduce a new mechanism [1] for ferroic order\, in which a non-zero quas
i-static magnetoelectric quadrupolar order appears due the coupling of flu
ctuating spin magnetic dipole moments and optical phonons. We show that ou
r proposed mechanism is consistent\, to our knowledge\, with many experime
ntal observations for the onset of the pseudo-gap phase in cuprate superco
nductors and therefore propose the quasi-static magnetoelectric quadrupole
as a possible pseudo-gap order parameter. By using first-principles calcu
lations in combination with our recent developed formalism [2]\, to calcul
ate multipole moments within a Berry phase approach\, we calculate the mag
nitude of the effect for the the prototypical cuprate superconductor\, HgB
a2CuO4+δ. Using these results we finally show that our mechanism embraces
several key findings of experimental reports and in addition also aspects
of previous theoretical models.\n\n[1] M. Fechner\, M. J. A. Fier
z\, F. Thöle\, U. Staub\, and N. A. Spaldin\, arXiv cond-mat.supr-con\, (
2015).\n\n[2] F. Thöle\, M. Fechner\, and N. A. Spaldin\, arXiv c
ond-mat.mtrl-sci\, (2016).
LOCATION:Staudingerweg 7\, room 01-327\, 55128 Mainz
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3476
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Yaroslav Pavlyu
kh on Non-equilibrium Electrons Dynamics as Observed in Time-Resolved Phot
oemission
DTSTART;VALUE=DATE-TIME:20160414T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3477@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Photoemission is a well established phenomenon and an instrume
nt for physical studies with more than a hundred years history (photoelect
ric effect). Thanks to recent advances in ultrafast lasers and streaking t
echniques it became possible [1\, 2] to trace the electron dynamics accomp
anying this process on the attosecond time-scale. In my talk I will addres
s from theoretical point of view the following facets of such dynamics: i)
time delay of electrons experiencing extrinsic and intrinsic energy losse
s [3] as observed in recent experiment on bulk Mg [4]\; ii) transient buil
d up of plasmonic excitations in C60 and emission of the secondary electro
n [5\,6]\; iii) long-lived quantum beatings resolved in time by two-photon
photoemission from antiferromagnetic NiO [7]. I will also briefly present
a methodological aspect of such studies\, namely propagation of the coupl
ed electron-boson Kadanoff-Baym equations describing the non-equilibrium e
lectrons dynamics.\n\n\nReferences:\n\n[1] R. Huber et al. How many-partic
le interactions develop after ultrafast excitation of an electron–hole p
lasma\, Nature 414\, 6861 (2001)\n\n[2] R. Pazourek\, S. Nagele\, and J. B
urgdörfer\, Attosecond chronoscopy of photoemission\, Rev. Mod. Phys. 87\
, 765 (2015)\n\n[3] M. Schüler\, J. Berakdar and Y. Pavlyukh\, Time-depen
dent many-body treatment of electron-boson dynamics: Application to plasmo
n-accompanied photoemission\, Phys. Rev. B 93\, 054303 (2016)\n\n[4] C. Le
mell et al. Real-time observation of collective excitations in photoemiss
ion\, Phys. Rev. B 91\, 241101(R) (2015)\n\n[5] M. Schüler\,Y. Pavlyukh\,
P. Bolognesi\, L. Avaldi\, and J. Berakdar\, Electron pair escape from fu
llerene cage via collective modes\, Scientific Reports 6\, 24396 (2016) \n
\n[6] Y. Pavlyukh\, M. Schüler and J. Berakdar\, Single- or double-electr
on emission within the Keldysh nonequilibrium Green's function and Feshbac
h projection operator techniques\, Phys. Rev. B. 91\, 155116 (2015)\n\n[7]
K. Satitkovitchai\, Y. Pavlyukh\, and W. Hübner\, Ab initio study of spi
n-orbit coupling effects on the low-lying excited states of NiO\, Phys. Re
v. B. 72\, 045116 (2005)
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3477
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: David Soriano o
n Spin Transport Phenomena in Graphene with Adatoms
DTSTART;VALUE=DATE-TIME:20160411T101500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3479@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Graphene has proven to be a perfect platform for electronic ap
plications (long mean free paths and electrons moving as massless Dirac fe
rmions). However\, its potential use in the field of spintronics has been
under debate during the last five years. The spin-orbit coupling induced b
y substrates and specific adatoms can reduce the spin relaxation time to t
he order of picoseconds making it useless for most spintronic applications
. \nIn this talk\, I will give a brief overview of spin dynamics in two di
fferent cases\, gold-decorated and magnetic hydrogenated graphene. In the
last part\, the possibility to induce a spin Hall type effect by Thallium/
Indium adatom segregation in graphene ribbons will be also discussed.
\n\nPseudospin-driven spin relaxation mechanism in graphene. D. Van Tuan\,
F. Ortmann\, D. Soriano\, S. O. Valenzuela and S. Roche. Nature Physics 1
0\, 857-863 (2014)\n\nMultiple quantum phases in graphene with enhance spi
n-orbit coupling: from quantum spin Hall regime to spin Hall effect and ro
bust metallic state. A. Cresti\, D. Van Tuan\, D. Soriano\, A. W. Cummings
and S. Roche. Phys. Rev. Lett. 113\, 246603 (2014) Spin transport in hydr
ogenated graphene. D. Soriano\, D. Van Tuan\, S. M.-M. Dubois\, M. Gmitra\
, A. W. Cummings\, D. Kochan\, F. Ortmann\, J.-Ch. Charlier\, J. Fabian an
d S. Roche. 2D Materials 2\, 022002 (2015) Spin dynamics and relaxation i
n graphene dictated by electron-hole puddles. D. Van Tuan\, F. Ortmann\, A
. W. Cummings\, D. Soriano and S. Roche. Scientific Reports 6\, 21046 (201
6)
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3479
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Bertrand Dupé
on Engineering magnetic skyrmions at transition-metal multilayers
DTSTART;VALUE=DATE-TIME:20160420T143000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3505@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Due to their unique topological and dynamic properties skyrmio
ns in magnetic materials offer attractive perspectives for future spintron
ic applications [1]. Recently\, it has been discovered that magnetic skyrm
ions of Néel-type symmetry cannot only occur in ultra-thin transition met
al films at surfaces [2\,3] but also in asymmetric multilayers due to stro
ng Dzyaloshinskii-Moriya (DMI) interactions [4]. We carry out first-princi
ples calculations in order to study the stabilization mechanism of skyrmio
ns from ultrathin films to multilayers and we predict the emergence of sky
rmions in a new class of multilayers based on [4d/Fe2/5d]n\, i.e. structur
es composed of Fe biatomic layers sandwiched between 4d- and 5d-transition
-metal layers [5]. In these composite structures\, the exchange and the Dz
yaloshinskii-Moriya interactions\, which control skyrmion formation\, can
be tuned separately by the two interfaces. This allows engineering skyrmio
ns as shown by density functional theory\, Monte Carlo and spin dynamics s
imulations.\n[1] A. Fert\, et al.\, Nature Nano. 8\, 152 (2013).\n[2] N. R
omming\, et al.\, Science 341\, 636 (2013).\n[3] B. Dupé\, et al.\, Natur
e Comm. 5\, 4030 (2014).\n[4] C. Moreau-Luchaire\, et al.\, Nature Nano. (
2016) doi: 10.1038/nnano.2015.\n[5] B. Dupé\, et al.\, accepted in Natur
e Comm. (arXiv :1503.08098).
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3505
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Mikhail Titov o
n Spin-orbit and spin-tranfer torques in two dimensions
DTSTART;VALUE=DATE-TIME:20160602T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3539@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Spin-orbit and spin-transfer torques are competing forces that
drive magnetic domains in the heavy-metal/ferromagnet bi-layers. In this
talk I present a microscopic theory of both effects that is naturally obta
ined from generalised Kubo formalism. In this formalism the torques are na
turally related to the spin-susceptibility tensors that can be evaluated m
icroscopically for a given model. Interestingly the formulation completely
avoids the notion of the spin current. I discuss the torques arising in t
he effective 2D Bychkov-Rashba model and speculate on various generalisat
ions of the results obtained.
LOCATION:Medienraum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3539
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Sarah Schroeter
on Skyrmion Caloritronics
DTSTART;VALUE=DATE-TIME:20160608T130000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3543@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We study how skyrmions in insulating chiral magnets can be man
ipulated by thermal currents. Thermal magnons couple efficiently to skyrmi
ons via an emerging magnetic field arising both from Berry phase effects a
nd spin-orbit coupling. This coupling gives rise to an intrinsic damping m
echanism for the skyrmion and to forces both parallel and perpendicular to
thermal gradients. In two dimensions we study the crossover from the ball
istic limit to the diffusive limit\, where magnons interact with defects\,
other magnons or phonons within the timescale needed to transverse the sk
yrmion. This crossover is described by a Boltzmann equation in relaxation
time approximation. We also investigate the magnon Hall effects arising fr
om the scattering from a finite density of skyrmions. Furthermore\, we dis
cuss the validity of semiclassical approximations and why stochastic Landa
u Lifshitz Gilbert equations are in general not suitable for caloritronics
applications.
LOCATION:Media Room
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3543
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Nils Richter on
Graphene Research Overview
DTSTART;VALUE=DATE-TIME:20160608T130000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3544@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Media Room
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3544
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Mikhail Raikh o
n Slow dynamics of spin pairs in random hyperfine field and organic magnet
o-resistance
DTSTART;VALUE=DATE-TIME:20160706T124500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3558@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The focus of the talk is the dynamics of spin-dependent recomb
ination in electron-hole pairs subject to external magnetic field\, B. Th
is recombination is at the core of the phenomenon of organic magnetoresist
ance (OMAR) in bipolar devices\, where recombination rate governs the pa
ssage of current via the spin-blocking process. Without recombination\, th
e spins of electron and holeprecess independently in effective fields b_e
+ B and b_h + B\, where b_e and b_h are the random hyperfine fields acting
on electron and hole\, respectively. In the presence of recombination\
, the precession acquires a correlated character due to the fact that the
carriers recombine only when their spins are in a singlet state. This c
orrelation\, in turn\, exerts a feedback on the recombination rate\, and c
onsequently\, on the current. Within the simplest transport model\, when t
he current flows through the system of parallel chains\, the sensitivity o
f current\,I\, to external field\, B\, is dominated by configurations of
b_e \, b_h for which the recombination is anomalously slow. We evalu
ate the statistical weights of these configurations and relate them to the
shape\, I(B)\, of the OMAR response.
LOCATION:Gernott-Gräff-Raum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3558
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Martin Stier on
Current-induced Skyrmion creation and Skyrmion fission
DTSTART;VALUE=DATE-TIME:20160706T134500
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3559@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic Skyrmions are considered to be topologically stable o
bjects. However\, in discrete lattices this topological protection is not
infinite but can actually be overcome. This means that Skyrmions can be cr
eated or destroyed. We show how this can be done theoretically by electric
al currents which may be either in in-plane or out-of-plane direction.
LOCATION:Gernott-Gräff-Raum
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3559
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Shufeng Zhang o
n Angular momentum transport in magnetic structures
DTSTART;VALUE=DATE-TIME:20160726T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3562@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Angular momentum (AM) currents in spintronics are carried by c
onduction electrons\, quasiparticle magnons\, as well as macroscopic order
-parameters. Depending on materials\, one or all of these carries contribu
te to the AM current. I will discuss these AMs in several structure and ma
terials. As an example\, we show how the AM propagates in antiferromagneti
c insulators and how the different types of AMs convert at interfaces. The
results will be compared with recent experiments.
LOCATION:Media Room
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3562
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Dmytro Bozhko o
n Bottleneck accumulation of hybrid bosons in a ferrimagnet
DTSTART;VALUE=DATE-TIME:20160802T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3565@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:An ensemble of spin wave quanta\, also known as magnons\, can
be treated as a Bose gas of weakly interacting quasi-particles. The excess
ive excitation of magnons in the system causes an increase in the chemical
potential of a thermalized magnon gas. When it becomes equal to the minim
al magnon energy a magnon Bose-Einstein condensate (BEC) may form at this
spectral point. However\, magnon-phonon interaction processes can signific
antly modify condensation scenario. Our observations of the magnon BEC in
a single-crystal film of yttrium iron garnet (Y3Fe5O12) by means of waveve
ctor-resolved BLS spectroscopy resulted in the discovery of a novel conden
sation phenomenon mediated by magneto-elastic interaction: A spontaneous a
ccumulation of hybrid magnon-phonon bosonic quasi-particles at the interse
ction of the lowest spin-wave mode and a transversal acoustic wave.
LOCATION:Medienraum\, 03-431
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3565
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Dr. Reza Mahani
on Magnetic solotronics near the surface of a semiconductor and a topolog
ical insulator
DTSTART;VALUE=DATE-TIME:20170131T143000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3689@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Technology where a solitary dopant acts as the active componen
t of an opto-electronic device is an emerging field known as solotronics\,
and bears the promise to revolutionize the way in which information is st
ored\, processed and transmitted.\nThe goal of the talk is in part to eluc
idate the properties of Mn impurities near the surface of GaAs semiconduct
ors with focus on their response to local magnetic and electric fields\, a
s well as to investigate the real-time dynamics of their localized spins.
The second part of the talk deals with the theoretical investigation of a
single substitutional Mn impurity and its associated acceptor state on the
(111) surface of Bi2Se3 topological insulator\, using combined Density fu
nctional theory and tight-binding calculations.\nThe quest to understand a
nd control\, at the atomic level\, how a few magnetic atoms precisely posi
tioned in a complex environment respond to external stimuli\, is the red t
hread that connects these two quantum materials in this talk.\nDepending o
n the time\, I could talk about the energy and magnetization transport in
non-equilibrium spin systems under both thermal gradient and external fiel
d.
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3689
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Volodymyr Kravc
huk on Effects of curvature in low-dimensional ferromagnetic nanosystems
DTSTART;VALUE=DATE-TIME:20170207T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3690@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Geometrical curvature results in new physical effects in low-d
imensional ferromagnetic systems.For1Dsystemswepredictthat: (i)atorsionind
ucedsymmetrybreakingappears in dispersion relation for magnons in a helix
shaped wire\; (ii) a local wire bend creates a pinning potential for a dom
ain wall\; (iii) the spin-current driven domain wall motion experiences th
e curvature induced shift of the Walker limit and the torsion induced shif
t of the nonadiabatic constant\, the latter can result in negative domain
wall mobility. For 2D systems we predict that: (i) magnetic skyrmion can b
e stabilized on a surface of revolution by curvature effects only\, even w
hen the intrinsic DMI is absent\; (ii) topological charge of a skyrmion ex
periences a shift\, which is determined by genus of the surface\, the latt
er results in topological triviality of magnetic skyrmion on a closed sphe
rical shell\; (iii) chirality symmetry breaking takes place in the vortex
polarity switching process for the case of a hemispherical shell. Most of
these effects can be treated as a result of the action of curvature induce
d DMI and anisotropy\, which effectively appear in exchange energy of a cu
rvilinear system.
LOCATION:Galilei room\, 01-128\, (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3690
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Joo-Von Kim on
Skyrmion dynamics in nanostructures: Breathing modes\, oscillators\, and t
he role of disorder
DTSTART;VALUE=DATE-TIME:20170214T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3691@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic skyrmions are nontrivial spin configurations that are
stabilised by chiral interactions. They are nanoscale objects with partic
le-like properties and are potentially useful for information storage and
processing. In this talk\, I will give an overview of our recent theoretic
al and numerical work on skyrmion dynamics in magnetic nanostructures. In
particular\, I will discuss breathing modes in dots\, self-sustained oscil
lations due to spin- transfer torques\, and the role of disorder for curre
nt-driven motion. I will discuss how these results could be useful for exp
erimental detection of skyrmions and their consequences for potential appl
ications.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3691
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Angelika Knothe
on Phase diagram of a graphene bilayer in the zero-energy Landau level
DTSTART;VALUE=DATE-TIME:20170221T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3692@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We theoretically investigate the ground state structure of bil
ayer graphene in the quantum Hall regime. In graphene bilayers\, a double
layer material formed of two atomic layers of graphene on top of each othe
r\, the states of the zero-energy Landau level carry\, besides the real sp
in\, two pseudospin degrees of freedom: a valley isospin and a Landau leve
l (n = 0\, n = 1) isospin. This peculiar property leads to an octet of sta
tes that is eightfold degenerate in the absence of any symmetry breaking a
nd can be treated in the frame of quantum Hall ferromagnetism. If this SU(
8) symmetry is indeed broken\, an extraordinary rich phase structure emerg
es\, each phase characterized by a different spin and isospin configuratio
n. Recent experiments [1] have revealed a plethora of transitions upon var
iation of the strength of an applied magnetic or electric field.\nWe start
from a four-band model Hamiltonian for Bernal stacked bilayer graphene an
d take into account both intrinsic symmetry breaking effects as well as th
e influence of externally applied electric and magnetic fields. Using a Ha
rtree-Fock treatment [2]\, we study the ground state spin and isospin phas
es as a function of external magnetic and electric field strengths. For th
e different filling factors of the zero-energy multiplet we predict the nu
mber of phases\, as well as the nature and the properties of the phases an
d the respective phase transitions [3].\n\n[1] J. Velasco Jr\, Y. Lee\, F.
Zhang\, K. Myhro\, D. Tran\, M. Deo\, D. Smirnov\, A. H. MacDonald\, and
C. N. Lau\, Nature Communications 5\, 4550 (2014)\; K. Lee\, B. Fallahazad
\, J. Xue\, D. C. Dillen\, K. Kim\, T. Taniguchi\, K. Watanabe\, and E. Tu
tuc\, Science 345\, Issue 6192\, pp. 58-61 (2014)\; Y. Shi\, Y. Lee\, S. C
he\, Z. Pi\, T. Espiritu\, P. Stepanov\, D. Smirnov\, C. N. Lau\, and F. Z
hang\, Phys. Rev. Lett. 116\, 056601 (2016)\; B. M. Hunt\, J. I. A. Li\, A
. A. Zibrov\, L. Wang\, T. Taniguchi\, K. Watanabe\, J. Hone\, C. R. Dean\
, M. Zaletel\, R. C. Ashoori\, and A. F. Young\, arXiv:1607.06461\,\n[2] J
. Lambert and R. Côté\, Phys. Rev. B 87\, 115415 (2013)\; K. Shizuya\, P
hys. Rev. B 86\, 045431 (2012) [3] A. Knothe and T. Jolicœur\, Phys. Rev.
B 94\, 235149 (2016)
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3692
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Marie Hervé on
Spin resolved scanning tunneling microscopy: Non-collinear magnetism and
high frequency dynamic properties
DTSTART;VALUE=DATE-TIME:20170328T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3726@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In magnetic thin films the Heisenberg exchange interaction oft
en leads to a parallel or antiparallel alignment of neighboring spins in t
he crystal. When inversion symmetry is broken e.g. by a surface or an inte
rface\, the non-collinear Dzyaloshinskii-Moriya interaction competes with
the Heisenberg exchange interaction. This competition can lead\, in some c
ase\, to the stabilization of complex spin textures such as spin spirals o
r skyrmions. Investigation of the local dynamic properties of magnetic str
uctures - such as skyrmion or nano-skyrmionic lattice - require the implem
entation of experimental technique with a high spatio-temporal resolution
(nm and sub-ns resolution). In this talk\, I will first show that spin-pol
arized STM (SP-STM) is an ideal tool to probe such non-collinear magnetic
structure. In a second part I will present our current progress in the dev
elopment of a new experimental technique combining ferromagnetic resonance
(FMR) with SP-STM.
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3726
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Daniele Pinna o
n Skyrmion Gas Manipulation for Probabilistic Computing
DTSTART;VALUE=DATE-TIME:20170404T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3730@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The topologically protected magnetic spin congurations known a
s skyrmions offer promising applications due to their stability\, mobility
and localization. In this work\, we emphasize how to leverage the thermal
ly driven dynamics of an ensemble of such particles to perform computing t
asks.\nWe propose a device employing a skyrmion gas to reshuffle a random
signal into an uncorrelated copy of itself. This is demonstrated by modell
ing the ensemble dynamics in a collective coordinate approach where skyrmi
on-skyrmion and skyrmion-boundary interactions are accounted for phenomeno
logically. Our numerical results are used to develop a proof-of-concept fo
r an energy efficient device with a low area imprint. Whereas its immediat
e application to stochastic computing circuit designs will be made apparen
t\, we argue that its basic functionality\, reminiscent of an integrate-an
d-fire neuron\, qualies it as a novel bio- inspired building block.
LOCATION:Galileo room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3730
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Peter Oppeneer
on Ultrafast magnetism: Recent theory developments
DTSTART;VALUE=DATE-TIME:20170516T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3765@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Ultrafast magnetism has become an area of intensive investigat
ions\, following the seminal discovery of ultrafast laser-induced demagnet
ization 20 years ago in Strasbourg. The fundamental mechanisms of ultrafas
t demagnetization have not unambiguously been uncovered and continue to be
debated.\nIn this seminar I shall present recent theoretical work that ai
ms to quantify how much spin-dissipation mechanisms such as Elliott-Yafet
electron-phonon spin-flip scattering\, ultrafast magnon generation and sup
erdiffusive spin transport could contribute.\nIn addition\, I shall discus
s other recent theoretical contributions to the field\, to mention\, ab in
itio theory for all-optical switching\, derivation of the Landau-Lifshitz-
Gilbert equation from the fundamental Dirac equation\, relativistic theory
of spin-photon interaction\, and recent theory to go beyond the two-tempe
rature model for describing femtosecond laser- excitation of solids.
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3765
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Jan Müller on
Skyrmions and topological charges in the helix
DTSTART;VALUE=DATE-TIME:20170523T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3766@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic skyrmions are whirls in the magnetization with an int
eger topological winding number. They are stabilized by exchange and Dzyal
oshinskii-Moriya interaction at scales down to the nanometer regime and tu
rn out to be highly stable and mobile. Due to these properties\, they are
often discussed as possible candidates for future memory devices. From a p
hysics perspective they are particularly interesting since new properties
emerge from the interplay of both energetic and topological contributions.
\nIn my talk I will mainly focus on topological defects in the helix\, whi
ch is another important phase that occurs in skyrmionic matter. It turns o
ut that a special kind of domain wall structure can occur between helical
phases with different orientations. The domain wall which connects the dif
ferently orientated helical phases\, can appear as a sequence of topologic
ally non-trivial disclinations and can be described within our phenomenolo
gical theory. Furthermore\, skyrmions also occur as the most natural defec
ts in the helical phase but they have different properties as their often-
studied counterparts in the polarized phase.
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3766
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Ulrike Ritzmann
on Motion of skyrmions and antiskyrmions driven by spin-orbit torques
DTSTART;VALUE=DATE-TIME:20170509T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3777@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Skyrmions are topologically stabilized spin structures on the
nanometer scale. They can be manipulated with electric current densities t
hat are orders of magnitude lower than those required for moving domain wa
lls. Especially\, isolated magnetic skyrmions can also occur in ultra-thin
transition metal films at surfaces and interfaces.\nWe have shown previou
sly that skyrmions exist in these systems due to a competition between mag
netic interactions beyond the first nearest neighbour approximation. We ha
ve found that this competition can stabilize higher order skyrmions in Pd(
fcc)/Fe/Ir(111) such as antiskyrmions (S=-1) and higher order antiskyrmion
s (S=-2).\nHere\, we present a study on the motion of these skyrmions via
spin transfer torques. The displacement of skyrmions can be described in a
rigid-body approximation\, whereas the motions of antiskyrmions require t
o take internal degrees of freedom into account.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3777
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Jonathan Chico
on Gilbert damping from first-principles methods
DTSTART;VALUE=DATE-TIME:20170613T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3801@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The Landau-Lifshitz-Gilbert (LLG) equation in combination with
first-principles methods\, has been used with great success to describe t
he magnetization dynamics in a wide range of cases and materials. Such as
the motion of magnetic textures\, e.g. domain walls and skyrmions\, and th
e description of magnetic excitations such as spin waves. Recent developme
nts have allowed for a more complete description of spin dynamics from fir
st principles thanks to the capacity to calculate the Gilbert damping from
ab-initio methods.\nIn the following talk a small overview of the most co
mmon methods used to determine the Gilbert damping from first principles w
ill be presented. The role of different considerations to the damping\, su
ch as the density of states at the Fermi level\, temperature\, chemical al
loying and the spin orbit coupling [1-3] will be presented making use of f
irst principles studies of materials of great technological importance suc
h as half-metallic Heusler alloys and permalloy.\n[1] J. Chico\, et al. Ph
ys. Rev. B 93\, 214439 (2016).\n[2] F. Pan\, J. Chico\, et al. Phys. Rev.
B 94\, 214410 (2016).\n[3] P. Dürrenfeld\, F. Gerhard\, J. Chico\, et al.
Phys. Rev. B 92\, 214424 (2015).
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3801
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Timo Kuschel on
Electrically and thermally induced spin currents in magnetic insulators
DTSTART;VALUE=DATE-TIME:20170620T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3813@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Spin currents in magnetic insulators are currently intensely i
nvestigated because of their potential to be the future information carrie
rs replacing part of the conventional charge current based electronics [1]
. Since there is no charge transport at all in magnetic insulators\, only
magnons\, the quanta of spin waves\, carry the spin information. Thus\, he
at dissipation is strongly reduced compared to the overall Joule heating o
f conventional charge transport. In order to connect the magnon spin syste
m with conventional charge current based electronics\, new techniques have
been developed to inject and detect magnon spins in magnetic insulators\,
e.g. Y3Fe5O12 (YIG) or NiFe2O4 (NFO). The spin Hall effect in heavy metal
s\, such as Pt\, next to a magnetic insulator is used to generate a magnon
spin current electrically\, while the thermal generation of magnon spin c
urrents is induced by the spin Seebeck effect [2\,3].\nIn my talk\, I will
show how the spin Hall effect and the spin Seebeck effect can be used to
generate and detect the spin transport in magnetic insulators in a local a
nd nonlocal experiment [4-7]. Thus\, we can observe quite long magnon spin
diffusion lengths of several microns in both YIG [4] and NFO [5]. Further
more\, I will explain that the transport of magnon spins through an insula
tor provides similar transport phenomena as electrons in a metal depending
on the direction of an external magnetic field. Here\, we found a magnon
anisotropic magnetoresistance in YIG that can be revealed in the nonlocal
experiment [6]. In addition\, I will show signatures of magnon-polarons in
the nonlocal magnon spin transport in YIG. These magnoelastic coupled mag
non-photon quasi particles have been recently detected via the local spin
Seebeck effect [8]\, but show even more surprising features in the nonloca
l experiment [7]. Finally\, going from ferrimagnetic to antiferromagnetic
insulators following the antiferromagnetic spintronics route [9]\, we coul
d find a sign change in the local spin Hall magnetoresistance for Pt on th
e easy-plane bulk antiferromagnet NiO [10]. Thus\, we are able to use the
spin Hall magnetoresistance as a probe to identify and study easy-plane an
tiferromagnetic materials.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3813
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Nadine Hauptman
n on Sensing skyrmions at the atomic scale combining magnetic exchange and
spin- polarized imaging
DTSTART;VALUE=DATE-TIME:20170627T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3814@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Recent developments in surface and interfacial magnetism have
raised the question if it is possible to realize a memory derived from sin
gle atoms or nanometer sized skyrmions. Therefore\, it is important to und
erstand how the local magnetic anisotropy driven by the crystal field symm
etry\, magnetic exchange\, and hybridization influences the magnetization
at the atomic length scale. Nevertheless\, a vast majority of atomic-scale
studies have utilized spin-polarized scanning tunneling microscopy (SP-ST
M)\, limiting the scope of materials which can be probed. In order to gain
new insight into magnetism at the atomic scale\, we combine SP-STM with m
agnetic exchange force microscopy (together called SPEX)\, based on a qPlu
s tuning fork design. We use SPEX to characterize the magnetic non-colline
ar nano-skyrmion structure of a single monolayer of Fe on Ir(111). We show
that SPEX is capable of disentangling structural from electronic or magne
tic effects\, which spin-polarized STM alone cannot achieve\, as well as p
robing direct and indirect magnetic exchange. Furthermore\, we use SPEX to
study the structure of the complex spin spiral dislocation network in the
second Fe layer on Ir(111).
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3814
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Filipe Guimarã
es on Dynamical amplification of magnetoresistances and Hall currents up t
o the THz regime
DTSTART;VALUE=DATE-TIME:20170704T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3815@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The quest for device miniaturization\, decreased energy consum
ption\, and improved speeds of processing and storage units naturally led
to exploiting the connection between electric currents and magnetization d
ynamics. In this presentation\, I demonstrate that ferromagnetic and antif
erromagnetic excitations can be triggered by the dynamical spin accumulati
ons induced by the bulk and surface contributions of the spin Hall effect
[1]. I also analyze the general concepts of magnetoresistance and Hall eff
ects together with spin-orbit- related mechanisms to demonstrate how dynam
ical currents can be dramatically enhanced and precisely controlled by app
lying ac electric fields and static magnetic fields\, in a materials- spec
ific approach [2]. Furthermore\, I uncover how pure spin currents generate
d by the spin Hall effect can be dynamically manipulated\, with effective
conversion rates increasing up to 500% and reaching values larger than the
giant ones obtained for static currents. The combination of in-silico mat
erial design and ultrafast dynamical effects is only achievable by a micro
scopic quantum mechanical theory\, utilizing an approach based on the elec
tronic structure. This work may also impact experimental techniques that u
se currents to probe and quantify magnetization precession and the torques
that induce it.\n[1] F. S. M. Guimarães et al.\, Phys. Rev. B 92\, 22041
0(R) (2015). [2] F. S. M. Guimarães et al.\, arXiv:1703.04493
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3815
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Akihiro Okamoto
on Dispersion and Berry curvature of spin wave in ferromagnets
DTSTART;VALUE=DATE-TIME:20170718T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3819@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Berry curvature is related to gauge field and studied in many
systems such as electron\, photon\, and quasi particles. One of interestin
g point to study Berry curvature of spin wave in ferromagnets is change of
effective interactions by sample geometry and thickness. In general\, Ber
ry curvature of spin wave is zero with only exchange interaction. Dipolar
interaction and Dyaloshinskii-Moriya interaction are well known to give ri
se to non-zero Berry curvature. Effective range and mechanism are differen
t between two interactions.\nWe recently calculated Berry curvature of spi
n waves in ferromagnetic films with dipolar and exchange interactions. In
this regime\, the exchange interaction makes the dispersion change depende
nt on the thickness. The resulting Berry curvature reproduces that in prev
ious works in the magnetostatic limit. In addition\, we found that the Ber
ry curvature of magnons in the dipole-exchange range has a peak at the cro
ssings of the eigen modes\, where hybridizations between the modes are sig
nificant.\nIn this presentation\, I introduce example of Berry curvature a
nd novel phenomena in some systems at first. After that\, I discuss Berry
curvature of spin wave in ferromagnets\, its application\, and possibility
at the last of presentation.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3819
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Imara L. Fernan
des on Impact of the chemical nature of defects on the pinning of magnetic
skyrmions
DTSTART;VALUE=DATE-TIME:20170808T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3823@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Owing to their topology\, magnetic skyrmions are considered as
potential particles for future information technology. However\, incorpor
ation of magnetic skyrmions as information carriers or memory storage unit
s in future information technology nodes requires a detailed understanding
of the impact of device imperfections on their speed\, motion\, creation
and stability. Following our previous studies [1\, 2]\, I will discuss fir
st-time fully ab-initio based simulations of single magnetic skyrmions in
Pd/Fe/Ir(111) surface interacting with 3d and 4d impurities and investigat
e the impact on the energetics\, electronic and magnetic properties. With
a careful analysis of the hybridization of the electronic states\, the imp
ortant mechanisms behind the expulsion or pinning of single magnetic skyrm
ions as function of the chemical nature of the impurities are identified.
I will highlight the universality of the skyrmions energy landscape when i
nteracting with transition metal defects and the possible impact on skyrmi
ons motion.\n[1] D. Crum\, et al. Nature Commun. 6\, 8541 (2015).\n[2] M.
Dos Santos Dias\, et al. Nature Commun. 7\, 13613 (2016).\nFunding provide
d by the European Research Council (ERC) under the European Union's Horizo
n 2020 research and innovation programme (ERC-consolidator grant 681405
— DYNASORE).
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3823
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Jonathan Leliae
rt on Thermally driven micromagnetic systems
DTSTART;VALUE=DATE-TIME:20170822T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3828@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Thermal fluctuations have always been a topic of interest in m
icromagnetism. Theoretical descriptions already date back to the fifties a
s W. F. Brown derived and presented the statistical properties of the rand
omly fluctuating thermal field required to physically describe the switchi
ng behaviour of single-domain nanoparticles. In this talk\, I present the
results of 2 studies on the measurement and simulation of thermally driven
magnetization dynamics.\nIn the first part\, the switching of magnetic na
noparticles is investigated via an experimental study\, introducing a new
method for magnetic nanoparticle characterization: Thermal magnetic noise
spectroscopy. Typically\, particle characterization is performed by measur
ing the particles’ response to an external excitation like an applied fi
eld. However\, such excitations are known to alter the nanoparticle’s ag
gregation state and thus affect the characterization results. Recently\, w
e demonstrated the feasibility of measuring the thermal magnetic noise emi
tted by magnetic nanoparticles in the absence of any excitation. The magne
tic particles’ noise spectrum was recorded using a SQUID in a magnetical
ly shielded environment and the recorded spectra could then be interpreted
in order to characterize the magnetic nanoparticles.\nThe second part of
the talk deals with the thermally activated motion of domain walls in a ma
gnetic nanowire. Because each finite-difference cell in micromagnetic simu
lations can be considered as a single-domain “particle”\, the thermal
field described by Brown can be added as an effective field term in the La
ndau-Lifshitz-Gilbert equation. Using large- scale micromagnetic simulatio
ns\, we explore the current-driven creep regime of a transverse domain wal
l in disordered Permalloy nanostrips. Our results show that the domain wal
l creep velocity exhibits a simple linear dependence on the current densit
y instead of the highly non-linear creep scaling law usually encountered i
n rough elastic systems. To explain this\, we derived an equation describi
ng the motion of a current-driven domain wall in a disordered nanowire at
finite temperatures. In contrast to the creep scaling law found in elastic
systems\, this equation is only valid for domain walls sufficiently small
to be described as rigid objects. We validated this equation against expe
rimental data and our micromagnetic simulations and could conclude that th
e domain walls under study can indeed be described as a rigid object inste
ad of an elastic line.\nThe ongoing miniaturization of spintronic devices
dictates that thermal effects will become increasingly important in microm
agnetic research\, and the two presented systems show that they can accura
tely be taken into account in numerical studies and can even be exploited
in technological applications.
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3828
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Nicolas Bachell
ier on Spin detection and doping of metallocenes on copper substrates
DTSTART;VALUE=DATE-TIME:20170815T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3838@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The main subject of this presentation will be the study of met
allocenes deposited on copper surfaces. Their adsorptions and electronic p
roperties are experimentally studied by scanning tunnelling microscopy (ST
M) and scanning tunnelling spectroscopy (STS). Our results were confirmed
by density functional theory (DFT) computations.\nMore precisely\, we stud
ied how ferrocene FeC10H10 and nickelocene NiC10H10 are adsorbed on copper
. We found that these metallocenes spontaneously create networks alternati
ng horizontal and vertical molecules. We added a cobalt atom to the ferroc
ene in order to modify its structure and we characterized the magnetic pro
perties of the new molecule we created\, in particular the appearance of a
Kondo effect showing that magnetic properties appeared in the molecule.\n
The spectroscopic study of nickelocene revealed an excitation of the molec
ule at low bias. This excitation consist in a change in the spin orientati
on of the molecule\, going from an orientation perpendicular to the main m
olecule axis to an orientation parallel to this axis. We finally transferr
ed a nickelocene to the STM tip and used this molecular tip to probe the s
tates of a second molecule. We consequently obtained a double spin excitat
ion in our tunnel junction\, with a significant increase of the conductanc
e due to excitations.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3838
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Roman Kováčik
on Spin disorder effect on the electronic and transport properties in mag
netic materials from first principles
DTSTART;VALUE=DATE-TIME:20171017T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3896@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The formation of a spin-disordered state due to the local mome
nt fluctuations at elevated temperatures strongly affects the ground state
electronic properties of magnetic materials. In particular\, we investiga
te how the spectral function changes as a function of temperature in selec
ted Heusler alloys. Furthermore\, we focus on the spin disorder effect on
the thermoelectric and spin-caloric transport properties in various magnet
ic nanostructures. This is motivated by the miniaturization of spintronics
devices and by recent suggestions that magnetic nanostructures can lead t
o extraordinary thermoelectric effects due to quantum confinement [1].\nIn
our approach\, the electronic structure is calculated within the full-pot
ential Korringa-Kohn-Rostoker Green function (KKR-GF) framework [2] using
the local density approximation. The Monte-Carlo methodology is used to si
mulate the effect of temperature induced spin disorder and the set of spin
-disordered configurations is fed back in the KKR-GF method to obtain the
statistical average of the relevant material properties [3-5].\n[1] N. Vu
et al.\, APEX 4\, 015203 (2011).\n[2] N. Papanikolaou et al.\, J. Phys.: C
ondens. Matter 14\, 2799\, (2002)\, also see: kkr-gf.org. [3] Ph. Mavropou
los et al.\, Phys. Rev. B 69\, 125104\, (2004).\n[4] R. Kováčik et al.\,
Phys. Rev. B 89\, 134417\, (2014).\n[5] R. Kováčik et al.\, Phys. Rev.
B 91\, 014421\, (2015).
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3896
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Davi R. Rodrigu
es on Effective description of topological magnetic textures
DTSTART;VALUE=DATE-TIME:20171024T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3929@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In this talk\, I will speak about magnetic textures including
domain walls and skyrmions in one and two dimensions from a macroscopic po
int of view. Among all the possible configurations\, there is a set of mag
netic textures with topological properties and a rather rigid structure. W
e analyze the minimum requirements for the existence and creation of these
textures. We will present an effective Hamiltonian formalism that describ
es the low energy excitation of the topological textures. This formalism i
s independent of microscopic details and external perturbations. We show h
ow interactions may be easily introduced and consider also antiferromagnet
ic materials. Future developments and potential applications will be discu
ssed.
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3929
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Oliver Breunig
on Gigantic negative magnetoresistance in a disordered Topological Insulat
or
DTSTART;VALUE=DATE-TIME:20171107T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3943@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Recently the phenomenon of negative magnetoresistance (MR) is
attracting renewed interest due to its occurrence in Weyl semimetals becau
se of the chiral anomaly. In other systems a large MR typically relates to
magnetism. In this talk a novel mechanism leading to a large negative MR
will be presented that is based not on magnetism\, but on disorder. In the
newly synthesized bulk- insulating topological insulator material T1BixSb
1-xTe2 we find a suppression of the resistivity by up to 98 % in 14 T at l
ow temperature. From transport data and numerical simulations\, this gigan
tic negative MR is understood by a percolation of charge puddles formed in
the disordered bulk.
LOCATION:Galileo room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3943
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Eric Bousquet o
n Magnetoelectric response from first- principles: microscopic understandi
ng and design rules
DTSTART;VALUE=DATE-TIME:20171122T150000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3958@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:First-principles calculations based on density functional theo
ry (DFT) appeared to be valuable tools to compute the strength of the magn
etoelectric response of materials and to understand its microscopic origin
. The methods are becoming sufficiently reliable and predictive to be used
in the search for new magnetoelectric materials.\nIn this talk I will pre
sent the state of the art of the different first-principles techniques tha
t can be used to compute the magnetoelectric response of a crystal under e
lectric or magnetic fields. I will show their applications on several syst
ems such as the prototypical magnetoelectric material Cr2O3\, LiFePO4 and
the troilite phase of FeS. For each of these systems\, I will discuss the
different microscopic mechanisms that drive their response: electronic ver
sus lattice mediated and spin versus orbital origins. Then\, I will presen
t two original examples of strain engineered ferroelectric and magnetoelec
tric responses in initially “non-functional” materials: CaMnO3 and NaM
nF3. I will also profit the occasion to introduce some related and exotic
features of magnetoelectricity: magnetoelectric monopoles and (ferro)toroi
dal moments.
LOCATION:ComZone 01-620 (Staudinger Weg 7)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3958
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Bernd Zimmerman
n on Spin-orbit effects from ab-initio theory: from electron scattering to
chiral spin textures
DTSTART;VALUE=DATE-TIME:20171205T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3961@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The spin-orbit interaction (SOI) is at the heart of spin orbit
ronics and gives rise to unique physical effects.\nThe vision is to exploi
t SOI for the generation\, transport and detection of spin currents withou
t magnetic fields\, i.e.\, the all-electric control of the electron spin\,
or to stabilize new magnetic states with non-trivial topology and novel p
roperties. Crucial from a materials perspective how much lattice defects\,
impurities and –in general– symmetry breaking alter such important sp
in-orbit effects like spin-relaxation\, the Hall effects and Dzyaloshinski
i-Moriya interaction (DMI).\nI will introduce the Korringa-Kohn-Rostoker (
KKR) method and focus on our new developments for the calculation of afore
mentioned spintronic effects with predictive power. I will show selected e
xamples to highlight the capabilities of our approach\, starting from our
discovery of a colossal anisotropy of spinrelaxation in metals [1-3]\, whi
ch originates from a pure band-structure effect. By explicitly including s
cattering properties off impurities\, we predict the electron skew-scatter
ing contribution to the Hall effects in ferromagnets for the first time [4
] and analyze complex disorder in the L10-ordered alloy FePt [5]. Finally\
, I will turn to magnetic interactions and highlight the importance of sym
metry-breaking for an anisotropic DMI\, which leads in a double-layer Fe o
n W(110) to the stabilization of anti-skyrmions rather than skyrmions\n[6]
. To conclude\, I will analyze the effect of intermixing on the DMI at the
prominent Co/Pt interface employing the powerful Coherent Potential Appro
ximation (CPA) for a disordered system [7].\n[1] Zimmermann et al.\, Phys
Rev. Lett. 109\, 236603 (2012)\, [2] Zimmermann et al.\, Phys. Rev. B 93\,
144403 (2016)\, [3] Long et al.\, Phys. Rev. B 90\, 064406 (2014)\, [4] Z
immermann et al.\, Phys. Rev. B 90\, 220403(R) (2014)\, [5] Zimmermann\, e
t al.\, Phys. Rev. B 94\, 060406(R) (2016)\, [6] Hoffmann et al.\, Nature
Commun. 8\, 308 (2017)\, [7] Zimmermann\, et al.\, in preparation.\nAll in
terested are cordially welcome!
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3961
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: André Thiavill
e on Skyrmions in symmetric bilayers
DTSTART;VALUE=DATE-TIME:20180122T130000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3963@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic skyrmions in ultrathin films require a strong chiral
interaction. It is usually provided by the Dzyaloshinskii-Moriya interacti
on\, of the interfacial type for ultrathin films. For single films\, in an
asymmetrical architecture\, it has been shown that the skyrmion size and
stability depend extremely sensitively on all sample parameters. Multilaye
rs with typically 10 repetitions of an asymmetrical structure have also be
ing studied\, showing robust skyrmions but\, as realized recently\, a degr
aded chirality of the domain wall due to magnetostatic effects.\nIn order
to retain\, by construction\, the benefits of both the magnetostatic inter
action and the Dzyaloshinskii-Moriya interaction\, we have studied symmetr
ic bilayers of ultrathin films\, each in an asymmetric structure. In such
a system\, we obtain robust skyrmions with a typical 100 nm diameter\, sho
w that they can be nucleated by localized current injection using sharp el
ectrodes\, measure their current-induced propagation with up to 60 m/s lon
gitudinal velocity\, and observe their transverse deflection according to
the gyrovector sign. These experiments were performed inside a magnetic fo
rce microscope. In addition\, high-resolution skyrmion shapes have been sy
stematically mapped using the NV-center magnetic microscope and the measur
ed distributions have been compared to micromagnetic simulations\, using a
physical description of magnetic disorder based on magnetic layer thickne
ss fluctuations.\n[1] Current-induced skyrmion generation and dynamics in
symmetric bilayers\, A. Hrabec\, J. Sampaio\, M. Belmeguenai\, I. Gross\,
R. Weil\, S.M. Cherif\, A. Stashkevich\, V. Jacques\, A. Thiaville\, and S
. Rohart\, Nat. Commun. 8\, 15765 (2017). [2] Skyrmion morphology in ultra
thin magnetic films\, I. Gross\, W. Akhtar\, A. Hrabec\, J. Sampaio\, L. J
. Martinez\, S. Chouaieb\, B. J. Shields\, P. Maletinsky\, A. Thiaville\,
S. Rohart\, and V. Jacques\, arXiv:1709.06027 (2017).
LOCATION:Media Raum\, 03-431 (Staudinger Weg 7)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3963
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Wojciech Morawi
ec on Master thesis talk: Specialization seminar
DTSTART;VALUE=DATE-TIME:20180109T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3967@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3967
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Igor Lukyanchuk
on Topological excitations in nano-scale ferroelectrics
DTSTART;VALUE=DATE-TIME:20180123T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3971@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Formation of unusual textures of polarization is imminent for
nano-scale ferroelectric samples\, films\, rods\, and granules\, where the
depolarization surface effects play the crucial role. The topologically p
rotected stability of such textures is coming from polarization vorticity\
, provided by condition of absence of the energetically-unfavorable depola
rization charge. Polarization domains that alternate the surface charge di
stribution\, first proposed by Landau and Kittel in contents of ferromagne
tism can be formed in ferroelectric thin films as an effective mechanism t
o confine the depolarization field to the near-surface layer and diminish
the depolarization energy. However\, their existence have long been consid
ered as barely possible until the direct theoretical predictions and exper
imental evidences thin oxide-based superlattices. Very recently we have de
monstrated that the effective capacitance of ferroelectric layers with dom
ains is negative. This effect is explained by the opposite orientation of
the depolarizing field with respect to the field-induced averaged polariza
tion. This phenomenon is currently considered as the platform for realizat
ion of the dissipationfree high performance nano-circuits. Moreover\, in s
ub-THz region the resonance plasmonic effect can be induced by oscillating
domain walls and can be suitable for design of the ultrasmall low-energy
THz chips. Multi-vortex and skyrmion states can be formed inside ferroelec
tric cylindrical nano-dots and nanorods to reduce the depolarization energ
y. We study the stability of such states and demonstrate that the topologi
cal class of the most stable topological excitations can be driven by the
geometrical and electrical parameters of the system\, external field and t
emperature. We target the multi-domain and topological excitations in FE n
anodots as a platform for multivalued logic units\, breaking ground for ne
uromorphic computing.\n\nAll interested are cordially welcome!
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3971
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Babak Seradjeh
on Universal fluctuations of Floquet topological invariants at low frequen
cies
DTSTART;VALUE=DATE-TIME:20180130T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3972@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3972
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Rafael Gonzalez
-Hernandez on Computational modeling of 2D materials beyond graphene
DTSTART;VALUE=DATE-TIME:20180227T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3990@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The last decade has seen nearly exponential growth in the scie
nce and technology of two-dimensional (2D) materials. Beyond graphene\, th
ere is a great variety of new monolayer materials\, which can adjust their
properties from insulators to superconductors. On the other hand\, the st
acking of different materials also allows an additional "dimensionality" i
n the design of new semiconductor and superconductor heterostructures. In
this talk\, I will discuss recent breakthroughs in the theoretical charact
erization of two-dimensional materials\, including the new 2D nitrides. In
particular\, starting from the wurtzite phase of gallium nitride (GaN)\;
mechanical\, electronic and optical properties of a novel 2D phase (type o
f graphene\, known as g-GaN) is debated. The structural and vibrational st
ability of g-GaN is presented within the density functional theory (DFT) f
ramework [1]. It is also shown a comparative study to reveal how their phy
sical properties are modified by the dimensionality and doping [2].\n\n[1]
P. Giannozzi\, et al\, J. Phys.: Condens. Matter\, (2009)\, 21\, 395502\n
[2] R. González\, W. López-Pérez\, Á. González-García\, M. Moreno-Ar
menta\, R. González-Hernández\, Applied Surface Science\, (2018) 433\, 1
049\n\nAll interested are cordially welcome!
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3990
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Kyoung-Whan Kim
on Chiral renormalization of magnetization dynamics through self-feedback
DTSTART;VALUE=DATE-TIME:20180306T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:3996@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Chiral magnets are ferromagnetic systems that prefer a particu
lar chirality due to the presence of spin-orbit coupling and broken invers
ion symmetry. They have received considerable attention due to their remar
kable properties including spin-orbit torque\, the Dzyaloshinskii-Moriya i
nteraction\, the existence of magnetic skyrmions\, and anisotropic magneto
resistance. Analysis of chiral magnets mostly starts from the Landau- Lifs
hitz-Gilbert equation with additional terms corresponding to the Dzyaloshi
nskii-Moriya interaction and the spin-orbit torque. In this formalism\, th
e chirality of equilibrium magnetic properties and that of non- equilibriu
m electron properties are only taken into account\, while that of non-equi
librium magnetic properties are not taken into account.\nIn this talk\, I
would like to present the effects of chirality on the excitation and relax
ation of magnetization. We examine self-feedback of chiral magnetization d
ynamics to demonstrate that the gyromagnetic ratio and the Gilbert damping
effectively felt by the magnetic moments depend on the chirality of magne
tic textures. We illustrate that the chiral renormalization of these param
eters is non-negligible for systems with large spin-orbit torque. We also
present how one can experimentally measure the chirality renormalized para
meters by the domain wall motion in the flow and creep regimes. The qualit
ative changes from the chiral renormalization indicate that describing the
dynamics of the magnetization in chiral magnets requires the chirality of
these parameters to be taken into account.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/3996
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Alexander Mook
on Topological Magnon Materials and Transverse Magnon Transport
DTSTART;VALUE=DATE-TIME:20180410T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4010@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The Topology has conquered the field of condensed matter physi
cs with the discovery of the quantum Hall effect. Since then the zoo of to
pological materials is steadily increasing. In this talk\, I demonstrate h
ow to realize different topological phases with magnons: the magnon pendan
ts to topological insulators as well as Weyl and nodal-line semimetals are
presented.\nMagnon bulk spectra are characterized by topological invarian
ts\, dictating special surface properties. For instance\, the bulk bands o
f topological magnon insulators (TMIs) carry nonzero Chern numbers\, causi
ng topological magnon edge states that revolve unidirectionally the sample
. Magnon Weyl semimetals possess zero-dimensional band degeneracies acting
as source and sink of Berry curvature\; at their surface they feature "ma
gnon arcs" connecting the surface projections of Weyl points. Magnon nodal
-line semimetals exhibit one-dimensional band degeneracies\, i. e.\, close
d loops in reciprocal space. Surface projections of these nodal lines host
"drumhead" surface states whose details depend strongly on the surface te
rmination.\nSimilar to the electronic case\, nonzero Berry curvature cause
s transverse transport\, that is\, magnon Hall effects. I show how these e
ffects can be quantified by classical spin dynamics simulations of the TMI
Cu(1\,3-benzenedicarboxylate) and a skyrmionic TMI.\nAll interested are c
ordially welcome!
LOCATION:Lorentz-Raum (Staudinger Weg 7\, 05-127)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4010
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Wojciech Morawi
ec on Master thesis talk: Method seminar
DTSTART;VALUE=DATE-TIME:20180417T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4058@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Wojciech Morawiec will give the second talk of his Master thes
is. The talk will be about the methodology that he will use during the res
earch phase of his master.
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4058
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Lykourgos Bouga
s on Ultrasensitive chiral sensing in the gas\, liquid\, and solid state b
y signal-reversing cavity polarimetry: applications to atmospheric studies
and biosensing
DTSTART;VALUE=DATE-TIME:20180515T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4073@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Chirality is a fundamental property of life\, making chiral se
nsing and analysis crucial to numerous scientific and technological fields
\, ranging from fundamental physics to drug development and food monitorin
g. The measurement of chiral optical rotation and circular dichroism is th
e most widely used method for chirality sensing\, but chiral signals are t
ypically very weak and their measurement is limited by larger time-depende
nt backgrounds and by imperfect and slow subtraction procedures. We’ll p
resent a novel cavity-enhanced polarimetric scheme that allows for: (a) th
e enhancement of the chiral signal by the number of the cavity passes (typ
ically »1000)\; (b) the suppression of birefringent backgrounds\; and (c)
the ability to reverse the sign of the chiral signal rapidly\, allowing f
or the isolation of the chiral signal from backgrounds and\, therefore\, i
ts absolute measurement. We’ll present measurements of optical rotation
for chiral molecules within achiral\, open-air\, environments\, and for ch
iral liquids in the evanescent wave produced by total internal reflection
at a prism surface. We’ll finally discuss different applications of our
technique with larger focus on atmospheric studies\, particularly the real
-time monitoring of chiral volatile organic compounds in forests\, and bio
molecular dynamics.\n\nAll interested are cordially welcome!
LOCATION:Galileo room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4073
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Paschalis Gkoup
idenis on Neuromorphic devices using organic materials
DTSTART;VALUE=DATE-TIME:20180605T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4080@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Hardware-based implementation of neuromorphic architectures of
fers efficient ways of data manipulation and processing\, especially in da
ta intensive applications such as big data analysis and real time processi
ng. In contrast to traditional von Neumann architectures\, neuro-inspired
devices may offer promising solutions in interacting with human sensory da
ta and process information in real time.\nTherefore such kind of devices m
ay offer in the future novel ways of data manipulation in bioelectronics.\
nOver the past years\, organic materials and devices have attracted lots o
f attention in bioelectronics due to their attractive characteristics for
bioelectronics applications such as biocompatibility\, the ability to oper
ate in liquid electrolytes\, tunability via chemical synthesis and low cos
t fabrication processes. \n\nHere\, various concepts of organic neuromorph
ic devices will be presented based on organic electrochemical transistors
(OECTs)\, devices that are traditionally used in bioelectronics. Regarding
the implementation of neuromorphic devices\, the key properties of the OE
CT that resemble the neural environment will be presented here. These incl
ude the operation in liquid electrolyte environment\, low power consumptio
n and the ability of formation of massive interconnections through the ele
ctrolyte continuum. Showcase examples of neuromorphic functions with OECTs
will also be presented\, including short-\, long-term plasticity and spat
iotemporal or distributed information processing.
LOCATION:Galileo room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4080
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Ilja Müller on
Master thesis talk: Method seminar "Theoretical Approach of Electron Tran
sport in Organic Semiconductors by the example of Organic Molecule PSSS"
DTSTART;VALUE=DATE-TIME:20180619T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4093@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4093
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Laura Köhler o
n Topological domain walls and dislocations in helimagnets
DTSTART;VALUE=DATE-TIME:20180703T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4094@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The Dzyaloshinskii-Moriya interaction in chiral magnets stabil
izes a magnetic helix with a wavelength set by the spin-orbit coupling. We
study domain walls of helimagnetic order both theoretically and experimen
tally using micromagnetic simulations and magnetic force microscopy studie
s on surfaces of FeGe. We find that such domain walls are distinctly diffe
rent from those in ferromagnets and rather similar to grain boundaries of
liquid crystals. Three types of domain walls are realized depending on the
relative domain orientation: a curvature wall\, a zig-zag disclination wa
ll and a dislocation wall.\nDisclinations are vortex defects in the helix
axis orientation\, and they can be combined to form dislocations. We discu
ss the topological skyrmion charge associated with these dislocations whic
h can be finite. This leads to an emergent electrodynamics and thus a coup
ling to spin currents as well as to a contribution to the topological Hall
effect. We discuss the dislocation profile using both micromagnetic simul
ations and an effective elasticity theory known from liquid crystals [2].
A single dislocation causes long-range distortions of the perfect helix. A
s a consequence\, impurities that pin the Goldstone mode have a strong imp
act on the dislocation motion.\nReferences\n[1] Schnherr et al. Topologica
l domain walls in helimagnets. Nat. Phys. 14\, 465 (2018)\n[2] Smalyukh\,
I. I.\, Lavrentovich\, O. D. Physical Review E 66\, 0511703 (2002)
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4094
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Mikhail Titov o
n Dzyaloshinskii-Moria interaction in Rashba systems
DTSTART;VALUE=DATE-TIME:20180626T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4095@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:We derive general finite temperature expressions for Dzyaloshi
nskii-Moriya interaction (DMI) and symmetric exchange in a 2D s-d ferromag
net model with momentum-dependent spin-orbit coupling (SOC) of Rashba type
and arbitrary (generally non-parabolic) kinetic energy of itinerant elect
rons. We show that a commonly used parabolic model with Rashba SOC gives r
ise to vanishing of both DMI and exchange stiffness in the metal regime\,
i.e. for both spin-split subbands occupied. Both quantities are\, however\
, finite if non-parabolic corrections to kinetic energy or non-linear corr
ections to SOC are taken into account. We further demonstrate that the com
monly assumed form of the DMI in terms of Lifshitz invariants breaks down
if SOC energy exceeds the s-d exchange energy. In this situation\, the DMI
vector becomes strongly anisotropic. It also acquires an additional essen
tial dependence on the perpendicular-to-the-plane component of the magneti
zation. We discuss the relevance of our results for the formation of chira
l magnetic textures in 2D systems with strong Rashba SOC.
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4095
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Jonas Nothhelfe
r on Magnetic Skyrmion materials as a platform for quantum information the
ory
DTSTART;VALUE=DATE-TIME:20180710T110000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4111@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Quantum Computation received great interest in the last years.
There two level systems\, in which the energy levels can be described as
effective spin up or spin down\, are used. The special feature here is\, t
hat the state of this two-level system is not forced to be either of the t
wo spin directions\, but also every superposition in between which is then
also known as a Qubit. Such Qubits form the basis of quantum information
theory\, a fully new paradigm of computation with still undisclosed potent
ial. In Spintronics systems topological protected spin-structures can be s
tabilized through the Dzyaloshinski-Moriya interaction. These objects are
called magnetic skyrmions\, which have many interesting properties and are
promising candidates for new applications. In my first Master talk\, I wi
ll introduce two ideas how magnetic skyrmion materials could potentially b
e used as a platform for quantum computation connecting these two fields.
The first idea is to exploit the excitation modes of skyrmions to define a
qubit analogous to the ones in Ion Trap quantum computers. The second ide
a is to use the topological properties of skyrmions for topological quantu
m computation.
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4111
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Vincent Baltz o
n Probing antiferromagnets with currents
DTSTART;VALUE=DATE-TIME:20180712T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4112@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4112
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: George Bouriano
ff on tba
DTSTART;VALUE=DATE-TIME:20181004T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4118@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4118
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Warlley Campos
on Semi-Transparent Particles in Optical Tweezers: Topological Insulators\
, Semiconductors and Generalization of the Ashkins Mode
DTSTART;VALUE=DATE-TIME:20181016T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4158@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:galilei Raum\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4158
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Imke Schneider
on Impurities and disorder in one-dimensional quantum systems
DTSTART;VALUE=DATE-TIME:20181030T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4165@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The effects of impurities in quasi one-dimensional quantum sys
tems are recently experiencing a renewed interest due to experimental real
izations in solid state systems and ultra-cold gases. Due to spatial confi
nement impurities have strong impact on the magnetic excitation spectrum a
nd transport properties in one dimension. Already the smallest generic sca
tterer can block the electric or magnetic conductance which leads to effec
tively isolated finite chain segments with discrete energies and character
istic boundary correlations. Surprisingly\, relatively little is known abo
ut impurity effects on the momentum- and frequency resolved dynamical resp
onse functions as for example the dynamical structure factor in spin-1/2 H
eisenberg chains. Using bosonization and the numerical Density Matrix Reno
rmalization Group we provide detailed quantitative predictions for the mom
entum and energy resolved structure factor in doped spin chains. Due to th
e impurities\, spectral weight is shifted away from the antiferromagnetic
wave-vector k = π into regions which normally have no spectral weight in
the thermodynamic limit. As another example of impurity physics in one dim
ension we consider simple intersections between one-dimensional quantum wi
res. These can act as coherent beam splitters for non-interacting electron
s. Here we examine how coherent splitting at such quantum wire crossings i
s affected by inter-particle interactions.
LOCATION:Galileo Room\, 01-128
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4165
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Markus Drescher
on The Theory of Inelastic Tunneling Spectroscopy in Superconductors
DTSTART;VALUE=DATE-TIME:20181106T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4180@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Tunnelling spectroscopy has been proven to be a powerful means
to determine fundamental properties of superconductors such as the densit
y of states\, with scanning tunnelling microscopy (STM) allowing for a hig
h spatial resolution. However\, data from STM experiments can in general o
nly be understood comprehensively by taking into account both elastic and
inelastic tunnelling processes. In inelastic tunnelling events\, the tunne
lling of the electron leads additionally to the excitation or annihilation
of collective bosonic modes such as phonons in the sample.\nWe extend the
theory of STM spectroscopy in superconductors by assuming that both the s
ample and the tip are in the superconducting regime and explore the charac
teristics of the system if inelastic tunnelling is taken into account. Bes
ides applying a constant voltage between sample and tip\, we also consider
an alternating sinusoidal voltage\, leading to Shapiro-like effects.\nAll
interested are cordially welcome!
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4180
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Inti Sodemann o
n The Berry curvature dipole and the shear sound of metals
DTSTART;VALUE=DATE-TIME:20181113T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4189@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:The Hall effect is often thought to be a hallmark of broken ti
me reversal invariance. I will describe how a Hall-like effect can appear
beyond linear response theory in time reversal symmetric metals. These met
als can have a non-linear Hall effect that is controlled by the "Berry cur
vature dipole": an average of the gradient of the Berry curvature over the
occupied states. I will describe recent experimental observation of this
effect in 2D materials and our predictions for the effect in 3D materials\
, including Weyl semimetals. I will also comment on the role of other extr
insic mechanisms and on an ongoing effort to try to understand the Berry d
ipole as a kind non-linear version of the Drude weight. If time permits\,
I will also describe our recent predictions of a novel shear collective mo
de in strongly interacting metals.
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4189
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Tobias Meng on
Weyl semimetals with single Weyl nodes\, and the fate of their chiral anom
aly
DTSTART;VALUE=DATE-TIME:20181120T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4190@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Weyl semimetals are defined by the presence of isolated points
in the Brillouin zone at which a conduction and a valence band touch. The
so-called Nielsen-Ninomiya theorem requires these points (the Weyl nodes)
to appear in pairs. This theorem\, however\, is only valid for interactio
ns of sufficiently short range. In this talk\, I will discuss that long-ra
nge interactions can break the Nielsen-Ninomiya-theorem\, and provide an e
xplicit construction for an interacting tight-binding model that contains
only a single Weyl node. I will then analyze the fate of the chiral anomal
y in such single Weyl node semimetals\, and demonstrate that the chiral ma
gnetic effect remains intact for arbitrarily strong interactions in such a
single node Weyl semimetal\, while it is at most robust up to a critical
interaction strength if the interaction gaps all Weyl nodes.
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4190
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Assa Auerbach o
n Equilibrium Formulae for Transverse Magneto-transport of Strongly Corre
lated Metals
DTSTART;VALUE=DATE-TIME:20181126T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4194@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In metals\, transport coefficients involve non-adiabatic relax
ational dynamics which are in general\, much harder to compute than equili
brium susceptibilities.\nIn this talk I present three formulas derived fro
m Kubo formula [1]\, for DC transport coefficients which can be expressed
as sums of equilibrium susceptibilities: (1) The Hall coefficient\, (2)
A modified Nernst coefficient\, and (3) The Thermal Hall coefficient. The
formulas are valid for general Hamitlonians and can treat bad metals w
here Boltzmann theory ceases to be valid. I show new results for the Hall
coefficients of the square lattice t-J model\, and of lattice bosons near
the Mott insulator phases.\n 1. Hall Number of Strongly Correlated Me
tals\, A. Auerbach\, Phys. Rev. Lett. 121\, 066601 (2018)
LOCATION:Lorentz Room 05-127 (Staudingerweg 7)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4194
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Maxime Garnier
on Many Majorana zero modes around the deformable edge of a magnetic skyrm
ion
DTSTART;VALUE=DATE-TIME:20181211T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4199@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic skyrmions are nanoscale particle-like spin configurat
ions that are efficiently created and manipulated. They hold great promise
s for next-generation spintronics applications. In parallel to thesedevelo
pments\, the interplay of magnetism\, superconductivity and spin-orbit cou
pling has proved to be a versatile platform for engineering topological su
perconductivity predicted to host non-abelianexcitations\, Majorana zero m
odes (MZMs).\nIn this talk\, after an introduction to topological supercon
ductivity and a quick survey of the experimental status of MZMs\, I will f
ocus on the theoretical analysis of magnetic skyrmions proximitized by con
ventional superconductors. We show that a topological superconducting phas
e can emerge in these systems and uncover a whole flat band of these modes
on the edge of the magnetic texture\, in contrast to a previously reporte
d MZM in the core of the skyrmion [1]. I will discuss in details the origi
n of these MZMs based on a procedure introduced in [2] that relates our pr
oblem to the the extensively-studied Rashba nanowire model [3\, 4]. We fin
d that these modes are remarkably stable to electronic and geometric pertu
rbations which we investigate by a combination of analytical arguments and
numerical tight-binding calculations. Additionally\, this analysis reveal
s that the number of MZMs on the edge scales linearly with its perimeter.
I will then discuss possible experimental realizations and consequences of
this phenomenon and argue that this system is suitable for the realizatio
n of the topological Kondo effect and of electron teleportation.\n\n[1] G.
Yang\, P. Stano\, J. Klinovaja & D. Loss\, PRB 93\, 224505 (2016). [2] F.
Wu & I. MArtin\, PRB 95\, 224503 (2017).\n[3] R. M. Lutchyn\, Jay D. Sau
& S. Das Sarma\, PRL 105\, 077001 (2010). [4] Y. Oreg\, G. Refael & F. von
Oppen\, PRL 105\, 177002 (2010)
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4199
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Anna Pertsova o
n Transient excitonic instability in optically-driven Dirac materials
DTSTART;VALUE=DATE-TIME:20190108T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4218@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In this talk\, I will firstly give a short summary of the rese
arch topics I have worked on over the past few years. This will include tw
o main subjects\, (i) development of computational methods for the descrip
tion of atomistic spin dynamics and time-dependent transport\, and (ii) in
vestigation of electronic and magnetic properties of Dirac materials (topo
logical insulators\, graphene\, Dirac/Weyl semimetals) in the presence of
external perturbations such as applied magnetic fields\, impurity doping a
nd optical excitations. I will then focus on our recent work on transient
excitonic condensate in optically-driven Dirac materials\, which is referr
ed to in the title of the talk. Motivated by recent pump-probe photoemissi
on experiments which demonstrate the existence of long-lived photo-excited
states in Dirac materials such as graphene and three-dimensional topologi
cal insulators\, we consider an optical pumping scheme which generates non
-equilibrium chemical potentials for electrons and holes. Such pumping com
bined with the Dirac nature of quasiparticles create favorable conditions
for excitoniccondensation. We identify experimental signatures of these ex
otic states and provide estimates for the size of excitonic gaps and criti
cal temperatures for few important examples of two- and three-dimensional
Dirac materials.\nAll interested are cordially welcome!
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4218
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Dr. Sayani Maju
mdar on Energy efficient ferroelectric tunnel junction memristors for neur
omorphic computing
DTSTART;VALUE=DATE-TIME:20190430T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4230@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4230
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Boerge Goebel o
n Going beyond skyrmions
DTSTART;VALUE=DATE-TIME:20190521T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4306@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic skyrmions are topologically non-trivial spin textures
which are stable at small sizes and which exhibit emergent electrodynamic
effects: they show a topological contribution to the Hall effect\, and ca
n be driven by currents. Skyrmions are considered as the bits in future da
ta storage devices\, where information can be stored very densely and acce
ssed with an enormous energetic efficiency. One issue\, which is hindering
the realization of this application\, is the so-called skyrmion Hall effe
ct: A skyrmion does not move parallel to an applied spin-polarized current
. Instead\, the skyrmion is pushed towards the edge of the sample where it
annihilates.\nIn this talk\, I will give an overview about the different
observed or proposed magnetic quasiparticles. The stabilization\, as well
as the emergent electrodynamic effects will be discussed for the antiferro
magnetic skyrmion [1]\, the skyrmionium [2]\, the bimeron [3]\, and the bi
skyrmion [4]. These magnetic objects are either remarkable from a fundamen
tal point of view\, or are advantageous application-wise. As an example\,
the antiferromagnetic skyrmion is understood as the combination of two sky
rmions with mutually reversed magnetic moments. The compensation of topolo
gical charge leads to the suppression of the skyrmion Hall effect for thes
e objects. Consequently\, the resulting velocity is drastically increased
when they are driven by currents.\nIncluded publications:\n\n[1] B. Gbel\,
A. Mook\, J. Henk\, I. Mertig. Phys. Rev. B. 96\, 060406(R) (2017).\n[2]
B. Gbel\, A. Schffer\, J. Berakdar\, I. Mertig\, S. Parkin. arXiv: 1902.06
295\n[3] B. Gbel\, A. Mook\, J. Henk\, I. Mertig\, O. Tretiakov. Phys. Rev
. B. 99\, 060407(R) (2019)\n[4] B. Gbel\, J. Henk\, I. Mertig. arXiv: 1902
.10491
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4306
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Calum Ross on M
agnetic skyrmions at critical coupling
DTSTART;VALUE=DATE-TIME:20190528T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4308@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:In a recent mathematical study of a family of models for magne
tic skyrmions in the plane a critical choice of couplings was found where
the models admit infinitely many explicit solutions [1]. These solutions s
atisfy first order Bogomol'nyi solutions and their energy is given in term
s of their degree. The explicit solutions are given in terms of an arbitra
ry holomorphic function. The simplest solutions are the basic Bloch and Ne
l skyrmions\, but we also exhibit distorted and rotated single skyrmions a
s well as line defects\, and configurations consisting of skyrmions and an
ti-skyrmions. Away from critical coupling I will give some examples of exp
licit axially symmetric solutions and an expression for their energy.\n\n[
1] Bruno Barton-Singer\, Calum Ross\, Bernd J Schroers\, https://arxiv.org
/abs/1812.07268\n\nAll interested are cordially welcome!
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4308
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Dr. Herbert Jae
ger on An introduction to Reservoir Computing
DTSTART;VALUE=DATE-TIME:20190604T133000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4309@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Recurrent neural networks (RNNs) are general approximators for
nonlinear dynamical systems and have recently become widely used in the "
deep learning" field of machine learning\, especially for speech and langu
age processing tasks. For instance\, Google's speech recognition and langu
age translation services are based on RNNs.\nHowever\, the deep learning s
et-ups for RNN training are computationally expensive\, require very large
volumes of training data\, and need high-precision numerical processing.
For such reasons\, deep-learning variants of RNNs are problematic in field
s where training data are scarce\, where fast and cheap algorithms are des
ired\, or where noisy or low-precision hardware is to be used. This is oft
en the case in domains of nonlinear signal processing\, control\, brain-ma
chine interfacing\, biomedical signal processing\, or unconventional (non-
digital) computing hardware.\nReservoir Computing (RC) is an alternative m
achine learning approach for RNNs which is in many ways complementary to d
eep learning. In RC\, a large\, random\, possibly low-precision and noisy
RNN is used as a nonlinear excitable medium - called the "reservoir" - whi
ch is driven by an input signal. The reservoir itself is not adapted or tr
ained.\nInstead\, only a "readout" mechanism is trained\, which assembles
the desired output signal from the large variety of random\, excited signa
ls within the reservoir. This readout training is cheap - typically just a
linear regression. RC has become a popular approach in research that aims
at useful computations on the basis on unconventional hardware (non-digit
al\, noisy\, low-precision).\nThe talk gives an introduction to the basic
principles and variants of RC. Illustrative examples will be selected acco
rding to wishes from the audience\n\nAll interested are cordially welcome!
LOCATION:MAINZ Seminarraum (Staudingerweg 9\, 03-122)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4309
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Ran Cheng on An
tiferromagnetic Magnons - A tale of two spins
DTSTART;VALUE=DATE-TIME:20190702T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4319@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnons\, the quanta of spin‐wave excitations\, can transpor
t spin angular momenta over long distances without incurring Joule heating
. They are promising alternatives to electrons in building next‐generati
on nanotechnology. To fully function as electrons\, however\, magnons shou
ld bear an intrinsic degree of freedom similar to the electron spin. In an
tiferromagnets\, spin‐up and spin‐down magnons coexist and form a uniq
ue degree of freedom capable of encoding information\, which can be contro
lled through the Dzyaloshinskii-Moriya interaction\, temperature gradient\
, etc. Guided by the resemblance between antiferromagnetic magnons and ele
ctrons with spin being an active variable\, we propose a series of physica
l phenomena where magnons can function as electrons in transporting and tr
ansferring spin angular momenta\, including magnon-induced interlayer coup
ling\, spin Nernst and spin Edelstein effects\, and magnonic spin torques
in an insulating spin valve with antiferromagnetic spacer. These phenomena
introduced a vibrant playground for new fundamental physics and opened th
e exciting possibility of utilizing magnons as primary information carrier
s in electronic devices.
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4319
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Xiong-Jun Liu o
n Emergent topology and symmetry-breaking order in correlated quench spin
dynamics
DTSTART;VALUE=DATE-TIME:20190705T130000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4320@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Quenching a quantum system involves three basic ingredients: t
he initial phase\, the post-quench target phase\, and the induced non-equi
librium dynamics which carries the information of the former two. In this
talk\, I will introduce how to characterize topological quantum phases by
far-from-equilibrium quantum dynamics induced by quench\, and further prob
e dynamically both the topology and symmetry-breaking orders in correlated
topological systems. The generic theory is established by showing a dynam
ical bulk-surface correspondence\, which connects the bulk topology of top
ological phases to dynamical topological pattern of quench dynamics emergi
ng in the so-called band-inversion surfaces (BISs) in momentum subspace\,
similar to the well-known bulk-boundary correspondence in the real space.
In the interacting regime\, we show that the complex (pseudo)spin dynamics
are governed by a microscopic Landau-Lifshitz-Gilbert-Bloch equation and
find that\, with the particle-particle interaction playing crucial roles\,
the correlated quench dynamics exhibit robust universal behaviors on the
BISs\, from which the nontrivial topology and magnetic orders can be extra
cted. In particular\, the topology of the post-quench system can be charac
terized by an emergent dynamical topological pattern of quench dynamics on
BISs\, which is robust against dephasing and heating induced by interacti
ons\; the pre-quench symmetry-breaking orders can be read out from a unive
rsal scaling of the quench spin dynamics emerging on the BIS\, which is va
lid beyond the mean-field approximation. These results may show insights i
nto the exploration of novel correlation physics with nontrivial topology
by quench dynamics.\n\nReferences:\n[1] L. Zhang\, L. Zhang\, S. Niu\, and
X.-J. Liu\, Science Bull. 63\, 1385 (2018).\n[2] W. Sun\, C.-R. Yi\, B.-Z
. Wang\, W.-W. Zhang\, B.C. Sanders\, X.-T. Xu\, Z.Y. Wang\, J. Schmiedmay
er\, Y. Deng\, X.-J. Liu\, S. Chen\, and J. -W. Pan\, Phys. Rev. Lett. 121
\, 250403 (2018).\n[3] B. Song\, C. He\, S. Niu\, L. Zhang\, Z. Ren\, X.-J
. Liu\, and G.-B. Jo\, arXiv:1808.07428\; Nature Physics\, in press (2019)
.\n[4] L. Zhang\, L. Zhang\, and X.-J. Liu\, Phys. Rev. A 99\, 053606 (201
9).\n[5] L. Zhang\, L. Zhang\, Y. Hu\, S. Niu\, and X.-J. Liu\, arXiv:1903
.09144v2.
LOCATION:Media Room 03-431 (Staudingerweg 7)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4320
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Nikolai A. Sini
tsyn on Integrable Time-Dependent Quantum Hamiltonians
DTSTART;VALUE=DATE-TIME:20190924T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4324@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Time-dependence of parameters provides a whole new dimension f
or engineering quantum systems with unusual behavior. The limits of fast a
nd slow (adiabatic) time-dependence are well studied. However\, the interm
ediate regime is very poorly understood today because of the lack of prope
r theoretical methods and efficient numerical algorithms. This is the plac
e where robust and unusual effects are still waiting to be uncovered. \nI
n this talk I will describe the method to study dynamics of interacting sp
ins with simple\, e.g.\, ~t or ~1/t time-dependence of some of the paramet
ers without any approximation. I define what it means for such systems to
be integrable and then show three examples that reveal robust dynamic effe
cts. One is the BCS model with decaying superconducting gap\, which shows
nonadiabatic emergence of a fully thermalized state. Another is the model
of cavity QED with linear optical frequency chirp\, which demonstrates a s
harp phase transition between fast and slow phases. The third model shows
the effect of dynamic spin localization in a hysteresis loop of interactin
g spins. This effect has no counterpart in any known classical or quantum
spin model. \nReferences: \n[1] NA Sinitsyn\, EA Yuzbashyan\, VY Chernyak\
, A Patra\, C Sun. Integrable time-dependent quantum Hamiltonians\, Phys.
Rev. Lett. 120 190402 (2018)\n[2] F Li\, VY Chernyak\, and NA Sinitsyn. Qu
antum annealing and thermalization: insights from integrability\, Phys. Re
v. Lett. 121\, 190601 (2018)
LOCATION:Lorentz Room 05-127 (Staudingerweg 7)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4324
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Joel Moore on O
rigin of strong and/or quantized optical properties of topological semimet
als
DTSTART;VALUE=DATE-TIME:20191218T100000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4423@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:This talk starts by reviewing known examples of how topologica
l materials generate new kinds of electrodynamic couplings and effects. T
hree-dimensional topological insulators realize a particular electromagnet
ic coupling known as “axion electrodynamics”\, and understanding this
leads to an improved understanding of magnetoelectricity in all materials.
We then turn to how topological Weyl and Dirac semimetals can show uniqu
e electromagnetic responses\; we argue that in linear response the main ob
servable effect solves an old problem via the orbital moment of Bloch elec
trons\, and how in nonlinear optics there should be a new quantized effect
\, which may have been seen experimentally. This nonlinear effect has a n
atural quantum e^3/h^2 and appears in chiral Weyl semimetals over a finite
range of frequencies. We discuss interaction and disorder corrections to
nonlinear responses in closing.\n\nWork with F. de Juan\, A. Grushin\, T.
Morimoto\, D. Parker\, J. Orenstein\, C. Felser\, T. Torchinsky\, and oth
ers.\n
LOCATION:Room 05-431 (Gernot-Gräff-Raum)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4423
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theory of Condensed Matter: Hard Condensed Matter: Souvik Paul on
First-Principles Study of Magnetic Skyrmions in Transition-Metal Ultrathi
n Films
DTSTART;VALUE=DATE-TIME:20200121T140000
DTSTAMP;VALUE=DATE-TIME:20240424T171129Z
UID:4431@iannounce.physik.uni.mainz.de
CATEGORIES:
DESCRIPTION:Magnetic skyrmions\, localized spin structure with topological
protection\, have become a research hotspot as they show promise for futu
re memory and logic devices. The key challenges for applications are to ac
hieve small bits and stability of those skyrmionic bits. Research shows th
at transition-metal interfaces (TMI) and multilayers are a very promising
class of systems to realize nanometer-sized and stable magnetic skyrmions.
Therefore\, a lot of effort has been put to tailor the properties of thes
e systems for application. \nIn this direction\, using first-principles me
thods\, we have proposed ultrathin films\, Fe/Rh and Rh/Fe bilayers on Re(
0001) substrate\, which show various spin structures at the interface incl
uding isolated skyrmions\, depending on the stacking order of Fe/Rh and Rh
/Fe bilayers. This study would encourage the experimentalist to check our
predictions and would generate more investigations on other bilayers on Re
(0001). \nThe other topic I would focus on is the effect of higher-order e
xchange interactions (HOI) on the stability of skyrmions. HOI are shown to
stabilize magnetic ground states in transition-metal ultrathin films\, ho
wever\, their role on the stability of metastable skyrmions has note been
investigated yet. We showed that the HOI increase the stability of skyrmio
ns by a large amount at TMI. This study opens up a route to tune skyrmions
stability and lifetime in ultrathin films. \n\n[1] Nat. Nanotechnol. 8\,
899–911 (2013)\n[2] Sci. Rep. 4\, 6784 (2014)\n[3] Nat. Commun. 5\, 4652
(2014)\n[4] arXiv:1912.03465\n[5] Nat. Phys. 7\, 713 (2011)\n[6] Phys. Re
v. Lett. 120\, 207201 (2018)\n[7] Phys. Rev. Lett. 120\, 207202 (2018)\n[8
] arXiv:1912.03474
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
URL:https://iannounce.physik.uni-mainz.de/meeting/user/event/4431
END:VEVENT
END:VCALENDAR