Hexagonal warping on optical conductivity of surface states in Topological Insulator Bi_{2}Te_{3}

TL;DR

This paper investigates how hexagonal warping in the surface states of Bi2Te3 topological insulators affects optical conductivity, revealing non-universal, energy-dependent behavior deviating from graphene-like responses.

Contribution

It demonstrates the impact of hexagonal warping on optical transitions and density of states, providing new insights into the electronic properties of Bi2Te3 surface states.

Findings

Optical conductivity increases quasilinearly with energy.

Hexagonal warping enhances the slope of conductivity and interband jump.

Density of states deviates downward from linear with energy.

Abstract

ARPES studies of the protected surface states in the Topological Insulator $% Bi_{2}Te_{3}$ have revealed the existence of an important hexagonal warping term in its electronic band structure. This term distorts the shape of the Dirac cone from a circle at low energies to a snowflake shape at higher energies. We show that this implies important modifications of the interband optical transitions which no longer provide a constant universal background as seen in graphene. Rather the conductivity shows a quasilinear increase with a slightly concave upward bending as energy is increased. Its slope increases with increasing magnitude of the hexagonal distortion as does the magnitude of the jump at the interband onset. The energy dependence of the density of states is also modified and deviates downward from linear with increasing energy.