Optical conductivity of Bismuth-based topological insulator

TL;DR

This study measures the optical conductivity of various Bismuth-based topological insulators across temperatures and frequencies, revealing how chemical compensation influences their electronic properties and charge carrier dynamics.

Contribution

It provides the first detailed analysis of how chemical compensation affects the optical spectra and charge carriers in Bismuth-based topological insulators.

Findings

Suppression of extrinsic Drude term with increased compensation

Appearance of absorption peaks from localized electronic transitions

Charge-carrier density estimated at ~10^17/cm^3 in highly compensated sample

Abstract

The optical conductivity and the spectral weight of four topological insulators with increasing chemical compensation (Bi2Se3, Bi2-xCaxSe3, Bi2Se2Te, Bi2Te2Se) have been measured from 5 to 300 K and from sub-THz to visible frequencies. The effect of compensation is clearly observed in the infrared spectra, through the suppression of an extrinsic Drude term and the appearance of strong absorption peaks, that we assign to electronic transitions among localized states. From the far-infrared spectral weight of the most compensated sample (Bi2Te2Se) one can estimate a density of charge-carriers in the order of 10^17/cm^3 in good agreement with transport data. Those results demonstrate that the low-energy electrodynamics in single crystals of topological insulators, even at the highest degree of compensation presently achieved, is still affected by extrinsic charge excitations.