Experimental Demonstration of Topological Surface States Protected by Time-Reversal Symmetry

TLDR

Scanning tunneling microscopy images reveal interference fringes from topological surface states scattered by Ag impurities and step edges on Bi₂Te₃(111). Direct STM imaging of standing waves on Bi₂Te₃(111) confirms a Dirac‑cone dispersion and demonstrates complete suppression of backscattering by nonmagnetic impurities, providing direct evidence of time‑reversal‑protected topological surface states.

Abstract

We report direct imaging of standing waves of the nontrivial surface states of topological insulator Bi2Te3 using a scanning tunneling microscope. The interference fringes are caused by the scattering of the topological states off Ag impurities and step edges on the Bi2Te3(111) surface. By studying the voltage-dependent standing wave patterns, we determine the energy dispersion E(k), which confirms the Dirac cone structure of the topological states. We further show that, very different from the conventional surface states, backscattering of the topological states by nonmagnetic impurities is completely suppressed. The absence of backscattering is a spectacular manifestation of the time-reversal symmetry, which offers a direct proof of the topological nature of the surface states.