Spin-dependent electronic structure and experimental techniques for its investigation
Mariia Filianina (St Petersburg State University, Russia)

Owing to its importance for spintronics effect of spin-orbit coupling (SOC) has attracted great attention in recent years. The most instructive is two-dimensional electron gas (2DEG), where SOC leads to spin-orbit splitting of the electronic states due to the Rashba effect [1]. Similarly, so called Rashba splitting was observed for surface states of several single crystals and quantum-well states in thin films, see for instance [2,3]. Spin-orbit coupling induced electronic structure plays an important role in the prospect of spintronics for generation and manipulation of spin currents. The most promising materials in this respect become well-known graphene and topological insulators (TIs), which are insulators in the bulk having metallic-like topological surface states. Electronic structure of free-standing graphene is featured by single Dirac-cone-like electronic states near K point of the SBZ, where the Dirac point is located directly at the Fermi level and the states are spin-degenerate [4]. The unique electronic structure of free-standing graphene can be achieved under intercalation of monolayer of heavy atoms underneath graphene, grown on various substrates [5]. Moreover, in such systems the spin degeneracy of electronic states was observed to be lifted because of strong SOC induced by both the intercalate and the substrate. Unlike graphene, TIs possess a single Dirac cone of electronic states with helical spin polarization, i.e. the topological surface states (TSSs) are spin non-degenerate [6]. This provide a possibility of spin-polarized conduction channels with less dissipation since scattering on non-magnetic impurity is forbidden in TIs [6]. Besides, the TSSs are believed to be topologically protected from any non-magnetic perturbation on the surface of TI.
One of the most powerful experimental techniques for studying electronic and spin structure of the systems is Spin- and Angle-Resolved Photoemission Spectroscopy (SARPES) in combination with synchrotron radiation. Analyzing angle and energy distributions of the emitted photoelectrons one can get information about initial electronic states in the sample, their dispersion in reciprocal space and, moreover, about spin structure using Mott detector [7]. Being a very surface sensitive technique, SARPES is perfect for studying surface or interface states and various low-dimensional systems.
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