Topological insulators are novel class of materials. They are bulk insulators or semiconductors, but exhibit a metallic electronic surface state. The appearance of this topological surface state is a consequence of the symmetry of the bulk material, and hence it necessarily forms on any surface of a topological insulator. This fact is sometimes referred to as topological protection.
The topological surface state has a characteristic spin structure which reflects a Dirac cone. The spin structure has immediate implications for electronic scattering between the two branches of the cone: back scattering from one branch to the other requires a spin flip and is thus strongly suppressed. Topological insulators are both model systems to study spin dynamics and candidates for spintronics applications.
We study the electronic structure and the electron dynamics of new topological insulator materials using time- and angle-resolved two-photon photo- electron spectroscopy. Conducting these experiments using circularly polarized light, information on the orbital momentum of the electronic states becomes accessible. The research is done within an international network of collaborations with theoretical physicists and experts in crystal growth.
D. Niesner, S. Otto, V. Hermann, T. Fauster, T. V. Menshchikova, S. V. Eremeev,
Z. S. Aliev, I. R. Amiraslanov, M. B. Babanly, P. M. Echenique, and E. V. Chulkov "Bulk and surface electron dynamics in a p-type topological insulator SnSb2Te4", Phys. Rev. B 89 081404 (2014). DOI: 10.1103/PhysRevB.89.081404
D. Niesner, S. Otto, Th. Fauster, E. V. Chulkov, S. V. Eremeev, O. E. Tereshchenkoc, K. A. Kokh "Electron dynamics of unoccupied states in topological insulators", J. Electron. Spectrosc. Relat. Phenom. 195 258 (2014). DOI: 10.1016/j.elspec.2014.03.013
D. Niesner, T. Fauster, S. V. Eremeev, T. V. Menshchikova, Yu. M. Koroteev, A. P. Protogenov, E. V. Chulkov, O. E. Tereshchenko, K. A. Kokh, O. Alekperov, A. Nadjafov, and N. Mamedov "Unoccupied topological states on bismuth chalcogenides", Phys. Rev. B 86 205403 (2012). DOI: 10.1103/PhysRevB.86.205403