Impact of high-frequency pumping on anomalous finite-size effects in three-dimensional topological insulators

TL;DR

This paper explores how intense high-frequency light can be used to control the electronic gap and surface state properties in thin three-dimensional topological insulators, revealing tunable and light-induced band inversion effects.

Contribution

It introduces a method to manipulate the surface state gap in topological insulators using high-frequency pumping, employing Brillouin-Wigner perturbation theory for analysis.

Findings

The surface state gap can be tuned by adjusting the pump intensity.

High enough pump intensity induces band inversion in surface states.

Both the gap and group velocity components are controllable via light.

Abstract

Lowering of the thickness of a thin-film three-dimensional topological insulator down to a few nanometers results in the gap opening in the spectrum of topologically protected two-dimensional surface states. This phenomenon, which is referred to as the anomalous finite-size effect, originates from hybridization between the states propagating along the opposite boundaries. In this work, we consider a bismuth-based topological insulator and show how the coupling to an intense high-frequency linearly polarized pumping can further be used to manipulate the value of a gap. We address this effect within recently proposed Brillouin-Wigner perturbation theory that allows us to map a time-dependent problem into a stationary one. Our analysis reveals that both the gap and the components of the group velocity of the surface states can be tuned in a controllable fashion by adjusting the intensity of the driving field within an experimentally accessible range and demonstrate the effect of light-induced band inversion in the spectrum of the surface states for high enough values of the pump.