Institut für Physik, Karl-Franzens-Universität Graz, Universitätsplatz 5, 8010, Graz, Austria.
Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany.
Adv Mater. 2020 Mar;32(10):e1906725. doi: 10.1002/adma.201906725. Epub 2020 Jan 30.
SmB 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 SmB 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 SmB .
SmB 最近作为第一个强关联拓扑绝缘体的候选材料引起了相当大的关注。这类材料有望带来全新的性质，如关联增强的体带隙或由自旋激发产生的费米面。然而，SmB 及其表面态是否具有拓扑性还是平庸性仍存在很大争议，而解决这一问题的关键是角分辨光电子能谱（ARPES）和扫描隧道显微镜（STM）结果之间存在重大分歧。在此，进行了一项结合 ARPES 和 STM 的实验。研究发现，STM 对比度强烈依赖于偏置电压，且在超过 1 V 时会反转其符号。结果表明，理解这种对比度反转是解决 ARPES 和 STM 结果之间差异的关键。特别是，扫描隧道谱反映了表面的低能电子结构，这支持了表面态的平庸起源和 SmB 的表面金属性。
