Herrmann, H.; Hlawenka, P.; Siemensmeyer, K.; Weschke, E.; Sánchez-Barriga, J.; Varykhalov, A.; Shitsevalova, N. Y.; Dukhnenko, A. V.; Filipov, V. B.; Flachbart, K.; Gabáni, S.; Rader, O.; Sterrer, M.; Rienks, E. D. L.: Contrast Reversal in Scanning Tunneling Microscopy and Its Implications for the Topological Classification of SmB6. Advanced Materials 32 (2020), p. 1906725/1-5
10.1002/adma.201906725
Open Accesn Version

Abstract:
SmB6 has recently attracted considerable interest as a candidate for the first strongly correlated topological insulator. Such materials promise entirely new properties such as correlation-enhanced bulk bandgaps or a Fermi surface from spin excitations. Whether SmB6 and its surface states are topological or trivial is still heavily disputed however, and a solution is hindered by major disagreement between angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM) results. Here, a combined ARPES and STM experiment is conducted. It is discovered that the STM contrast strongly depends on the bias voltage and reverses its sign beyond 1 V. It is shown that the understanding of this contrast reversal is the clue to resolving the discrepancy between ARPES and STM results. In particular, the scanning tunneling spectra reflect a low-energy electronic structure at the surface, which supports a trivial origin of the surface states and the surface metallicity of SmB6.