Imaging of the valence band electronic structure of Cu(111) and Cu(100) surfaces and magnetic Co/Cu(100) films using the Spin-momentum-microscope
Dr. Christian Tusche (MPI, Halle)

Knowledge of the detailed electronic structure in the entire Brillouin zone and in the whole valence-band regime is a prerequisite for understanding new effects at surfaces. This information is obtained with unprecedented efficiency by a momentum microscope. This instrument directly images the parallel momentum distribution of photoelectrons using a photoelectron microscope (PEEM) in combination with an aberration-corrected energy analyzer.
The valence-band structure of the paradigmatic systems Cu(111) and Cu(100) was mapped over the complete first surface Brillouin zone by recording 200 constant- energy momentum distributions. The measurements provide simultaneous access to extended parts of the momentum space beyond high-symmetry regions, and serve as a testing ground for theoretical photoemission from bulk and surface states. For instance, we obtain quantitative agreement of the experiment to calculations within a one-step photoemission theory by improving the treatment of the d-bands which are incompletely described within the local density approximation.
We also added a spin-polarizing electron mirror at the exit of the energy filter [1]. As electrons are reflected in the (00) LEED spot of a W(100) single crystal surface, the full two-dimensional image information is preserved in the reflected beam, and image contrast proportional to the spin-polarization of the photoelectrons is obtained. In the spatial imaging mode, spin-resolved PEEM images of the magnetic domain structure of ultra-thin Co films were recorded. The parallel measurement of 3800 discrete image points further allows the efficient measurement of spin-resolved photoelectron momentum maps. Examples are given for the mapping of the spin-polarized quantum well state in few atomic layers thick Co films on Cu(100).

[1] Tusche, Ellguth, Ünal, Chiang, Winkelmann, Krasyuk, Hahn, Schönhense, Kirschner: Appl. Phys. Lett. 99, 032505 (2011)

*) This work was done in collaboration with M. Ellguth, A. Ünal, C.-T. Chiang, A. Winkelmann, J. Henk, A. Krasyuk, and J. Kirschner