Scanning tunneling microscopy study of the possible topological surface states in BiTeCl

TL;DR

This study uses low-temperature scanning tunneling microscopy to investigate the surface states of BiTeCl, providing evidence for topological surface states and clarifying previous conflicting reports about its topological nature.

Contribution

The paper presents direct STM evidence of topological surface states in BiTeCl, resolving previous discrepancies from photoemission and theoretical studies.

Findings

Evidence of topological surface states in low-defect BiTeCl surfaces

Different surface state behaviors observed in high-defect samples

Supports BiTeCl as a potential topological insulator

Abstract

Recently, the non-centrosymmetric bismuth tellurohalides such as BiTeCl are being studied as possible candidates of topological insulators. While some photoemission studies showed that BiTeCl is an inversion asymmetric topological insulator, others showed that it is a normal semiconductor with Rashba splitting. Meanwhile, first-principle calculationsfailed to confirm the existence of topological surface states in BiTeCl so far. Therefore, the topological nature of BiTeCl requires further investigation. Here we report low temperature scanning tunneling microscopy study on the surface states of BiTeCl single crystals. On the tellurium-terminated surfaces with low defect density, strong evidences for topological surface states are found in the quasi-particle interference patterns generated by the scattering of these states, both in the anisotropy of the scattering vectors and the fast decay of the interference near step edges. Meanwhile, on samples with much higher defect densities, we observed surface states that behave differently. Our results help to resolve the current controversy on the topological nature of BiTeCl.