Abstract:
In the present work, the electronic structure of samarium hexaboride (SmB6), a socalled Kondo-Insulator, has been investigated by means of angle-resolved photoemission spectroscopy (ARPES). In particular, the aim was to clarify whether SmB6 is a topological insulator. As typical for a Kondo insulator at low temperature, SmB6 develops an insulating bulk band gap by hybridisation between Sm 5d and Sm 4f orbitals, whereby the material becomes insulating. At the surface, however, a residual conductivity remains, which, in literature, is attributed to topological surface states. Supported by theoretical models and experimental indications - as for example the robustness of conductivity against adsorbates and a Fermi surface topology with electronic states at ¯X - SmB6 was established as first strongly correlated topological insulator. In context of this work, however, it could be shown, that the residual conductivity at the surface is caused by trivial states. That was done, among others, by surface modification and temperature studies. Basis is the identification of two discrete surface determinations along the (100) plane, namely a Boron and a Samarium termination. The assignment is based on the Boron 1-s- and the Samarium 4-f-core level structure. Subsequently, two surface states are characterised for both terminations: At the ¯ 􀀀 point of the surface Brillouin zone, a trivial state within the bulk band gap could be identified. This state shows a Rashba splitting for Boron termination. For Samarium termination, however, it is spin degenerated. At both ¯X points another surface state could be assigned to a trivial origin, induced by a changed surface potential compared to the volume. Thereby, the f-d-resonance is shifted to higher binding energies for Boron termination and to lower for Samarium termination, respectively. In both cases, the Fermi energy becomes occupied and the surface conducting. The Samarium atoms of the f-d-resonance, however, are not localised at the topmost layer but for both terminations in the last fully coordinated Samarium layer. Thereby, the robustness of the state against residual gases, that has been assigned in literatue to a topological order, is explainable. By multiple arguments, a topological non-trivial scenario is not just excluded, but consistency on the hitherto existing results in literature was reached.