Surface Step Defect in 3D Topological Insulators: Electric Manipulation of Spin and Quantum Spin Hall Effect

TL;DR

This paper investigates how step defects on the surface of 3D topological insulators influence surface states, revealing controllable spin manipulation and the emergence of quantum spin Hall effect through electric gating.

Contribution

It introduces a detailed analysis of surface state spectra near step defects, demonstrating electric control of spin and the realization of quantum spin Hall effect in topological insulators.

Findings

Landau levels form on flat surface regions away from the defect

Electron spin can be arbitrarily manipulated by gate voltage during transport

Quantum spin Hall effect appears in high Landau level subbands

Abstract

We study the influence of step defect on surface states in three-dimensional topological insulators subject to a perpendicular magnetic field. By calculating the energy spectrum of the surface states, we find that Landau levels (LLs) can form on flat regions of the surface and are distant from the step defect, and several subbands emerge at side surface of the step defect. The subband which connects to the two zeroth LLs is spin-polarized and chiral. In particular, when the electron transports along the side surface, the electron spin direction can be manipulated arbitrarily by gate voltage. And no reflection occurs even if the electron spin direction is changed. This provides a fascinating avenue to control the electron spin easily and coherently. In addition, regarding the subbands with high LL index, there exist spin-momentum locking helical states and the quantum spin Hall effect can appear.