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. Ünal, C.-T. Chiang, A. Winkelmann, A.Krasyuk, M. Hahn, G. Schönhense, 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)
