Electron states on the smooth edge of 2D topological insulator: elastic backscattering and light absorption

TL;DR

This paper investigates the electronic and optical properties of edge states in 2D topological insulators with smooth boundaries, revealing conditions for backscattering, optical transitions, and conductance characteristics.

Contribution

It introduces a detailed analysis of edge states within the Volkov-Pankratov model, highlighting the effects of smooth edges on backscattering and optical absorption in 2D TIs.

Findings

Linear edge states exhibit topological protection with no backscattering.

Backscattering occurs when linear states overlap with Dirac states.

Drude-like conductivity appears when linear and Dirac states coexist.

Abstract

The 2D TI edge states are considered within the Volkov-Pankratov (VP) Hamiltonian. A smooth transition between TI and OI is assumed. The edge states are formed in the total gap of homogeneous 2D material. A pair of these states are of linear dispersion, others have gapped Dirac spectra. The optical selection rules are found. The optical transitions between the neighboring edge states appear in the global 2D gap for the in-plane light electric field directed across the edge. The electrons in linear edge states have no backscattering, that is indicative of the fact of topological protection. However, when linear edge states get to the energy domain of Dirac edge states, the backscattering becomes permitted. The elastic backscattering rate is found. The Drude-like conductivity is found when the Fermi level gets into the energy domain of the coexistence of linear and Dirac edge states. The localization edge conductance of a finite sample at zero temperature is determined.