# Current-induced gap opening in interacting topological insulator surfaces

## TL;DR

This paper demonstrates that in interacting topological insulator surfaces, an applied current can induce a gap in the edge or surface states by breaking time-reversal symmetry, leading to nonlinear conductance effects.

## Contribution

It reveals a novel mechanism where electron interactions and spin polarization cause current-induced gap opening in topological insulator edges and surfaces.

## Key findings

- Current induces a gap in helical edge states.
- Gap opening causes nonlinear I-V characteristics.
- Mechanism applicable to 3D topological insulator surfaces.

## Abstract

Two-dimensional topological insulators (TIs) host gapless helical edge states that are predicted to support a quantized two-terminal conductance. Quantization is protected by time-reversal symmetry, which forbids elastic backscattering. Paradoxically, the current-carrying state itself breaks the time-reversal symmetry that protects it. Here we show that the combination of electron-electron interactions and momentum-dependent spin polarization in helical edge states gives rise to feedback through which an applied current opens a gap in the edge state dispersion, thereby breaking the protection against elastic backscattering. Current-induced gap opening is manifested via a nonlinear contribution to the system's $I-V$ characteristic, which persists down to zero temperature. We discuss prospects for realizations in recently discovered large bulk band gap TIs, and an analogous current-induced gap opening mechanism for the surface states of three-dimensional TIs.