Experimental demonstration of the topological surface states protected by the time-reversal symmetry

TL;DR

This paper provides direct imaging evidence of topological surface states in Bi$_2$Te$_3$, demonstrating their unique scattering properties and confirming their Dirac cone dispersion, which is protected by time-reversal symmetry.

Contribution

The study offers the first direct visualization of topological surface states and their scattering behavior, confirming their Dirac cone structure and immunity to backscattering.

Findings

Backscattering of topological states is suppressed by nonmagnetic impurities.

Energy dispersion confirms Dirac cone structure.

Direct imaging of standing waves on Bi$_2$Te$_3$ surface.

Abstract

We report direct imaging of standing waves of the nontrivial surface states of topological insulator Bi$_2$Te$_3$ by using a low temperature scanning tunneling microscope. The interference fringes are caused by the scattering of the topological states off Ag impurities and step edges on the Bi$_2$Te$_3$(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, the 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.