Time-reversal invariant resonant backscattering on a topological insulator surface driven by a time-periodic gate voltage

TL;DR

This paper investigates how a time-periodic gate voltage induces resonant backscattering in topological insulator surface states without breaking time-reversal symmetry, revealing new spectral features and persistent spin-momentum locking.

Contribution

It demonstrates that Floquet sideband degeneracies enable TR-invariant resonant backscattering, offering a novel method to engineer Dirac spectra on topological insulator surfaces.

Findings

Resonant backscattering occurs without TR symmetry breaking.

Energy spectrum reshaped by periodic driving differs from circular polarization effects.

Spin precession law remains unchanged despite modified scattering processes.

Abstract

We study the scattering of the Dirac electrons by a point-like nonmagnetic impurity on the surface of a topological insulator, driven by a time-periodic gate voltage. It is found that, due to the doublet degenerate crossing points of different Floquet sidebands, resonant backscattering can happen for the surface electrons, even without breaking the time-reversal (TR) symmetry of the topological surface states (TSSs). The energy spectrum is reshuffled in a way quite different from that for the circularly polarized light, so that new features are exhibited in the Friedel oscillations of the local charge and spin density of states. Although the electron scattering is dramatically modified by the driving voltage, the $1/\rho$ scale law of the spin precession persists for the TSSs. The TR invariant backscattering provides a possible way to engineer the Dirac electronic spectrum of the TSSs, without destroying the unique property of spin-momentum interlocking of the TSSs.