物構研談話会（15-04）

概要

要旨: One of the fundamental concepts in solid state physics is the
description of the degrees of freedom of the electrons in the solid by
the relation of the energy E vs. the crystal momentum k in a band
structure of quasi particles. Of particular importance is the spin of
the electron that leads to phenomena like ferromagnetism,
spin-polarized surface- and interface-states, and recently, the
discovery of new material classes like topological insulators. The
latter attracted wide interest by the unusual relations of
electron-spin and -momentum. Only recently, experimental access to the
spin resolved band structure at every point in the Brillouin zone
became feasible by spin-resolved momentum microscopy [1]. This novel
concept combines high resolution imaging of photoelectrons in
two-dimensional (kx, ky) sections of the band structure with a highly
efficient imaging spin filter [2], and provides comprehensive
quantitative information beyond high-symmetry directions.

In topological insulators spin polarization is governed by strong
spin-orbit coupling. We show that this leads to a rich band-structure
of highly polarized states within the complete Brillouin zone of
Bi2Se3, beyond the well known "Dirac cone" surface state. For the
latter we find that the spin polarization of photoelectrons can reach
more than 90%. A direct conclusion on the ground state polarization in
these systems is complicated by the peculiar interplay between spin-
and light-polarization in the photoemission, as directly observed in
spin-resolved (kx, ky) images. Modifications of the electronic
structure by adsorbates and surface doping can be directly tracked by
the efficient measurement scheme [3], and are highly important for
potential applications of these materials.

[1] C. Tusche, A. Krasyuk, J. Kirschner: Ultramicroscopy (2015),
doi:10.1016/j.ultramic.2015.03.020
[2] C. Tusche, M. Ellguth, A. A. 扤nal, C.-T. Chiang, A. Winkelmann, A.
Krasyuk, M. Hahn, G. Sch扤nhense, J. Kirschner: Appl. Phys. Lett. 99,
032505 (2011)
[3] S. Roy, H. L. Meyerheim, A. Ernst, K. Mohseni, C. Tusche, M. G.
Vergniory, T. V. Menshchikova, M. M. Otrokov, A. G. Ryabishchenkova,
Z. S. Aliev, M. B. Babanly, K. A. Kokh, O. E. Tereshchenko, E. V.
Chulkov, J. Schneider, J. Kirschner: Phys. Rev. Lett. 113, 116802
(2014)
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