Driven Electronic States at the Surface of a Topological Insulator

TL;DR

This paper investigates how external light influences the electronic surface states of topological insulators, revealing polarization-dependent effects and new spectral features, with results aligning well with recent experiments.

Contribution

It provides a comprehensive theoretical analysis of non-equilibrium surface excitations under light, including polarization effects and novel spectral phenomena.

Findings

Circularly polarized light gaps out surface states.

Linear polarization induces an anisotropic metallic state.

Identification of shadow Dirac cones in spectral function.

Abstract

Motivated by recent photoemission experiments on the surface of topological insulators we compute the spectrum of driven topological surface excitations in the presence of an external light source. We completely characterize the spectral function of these non-equilibrium electron excitations for both linear and circular polarizations of the incident light. We find that in the latter case, the circularly polarized light gaps out the surface states, whereas linear polarization gives rise to an anisotropic metal with multiple Dirac cones. We compare the sizes of the gaps with recent pump-probe photoemission measurements and find good agreement. We also identify theoretically several new features in the time-dependent spectral function, such as shadow Dirac cones.