Optical properties of BiTeBr and BiTeCl

TL;DR

This study compares the optical and vibrational properties of BiTeBr and BiTeCl, revealing similar optical behaviors, Rashba splitting, and electron-phonon interactions, with notable differences in phonon intensities and doping levels.

Contribution

It provides a detailed comparative analysis of the optical and vibrational spectra of BiTeBr and BiTeCl, highlighting similarities and differences in their electronic and phononic properties.

Findings

Both materials are doped semiconductors with similar Rashba splitting.

Distinct differences in infrared phonon intensities and doping levels.

Identification of interband transitions, including a common low-energy Rashba-related transition.

Abstract

We present a comparative study of the optical properties - reflectance, transmission and optical conductivity - and Raman spectra of two layered bismuth-tellurohalides BiTeBr and BiTeCl at 300 K and 5 K, for light polarized in the a-b planes. Despite different space groups, the optical properties of the two compounds are very similar. Both materials are doped semiconductors, with the absorption edge above the optical gap which is lower in BiTeBr (0.62 eV) than in BiTeCl (0.77 eV). The same Rashba splitting is observed in the two materials. A non-Drude free carrier contribution in the optical conductivity, as well as three Raman and two infrared phonon modes, are observed in each compound. There is a dramatic difference in the highest infrared phonon intensity for the two compounds, and a difference in the doping levels. Aspects of the strong electron-phonon interaction are identified. Several interband transitions are assigned, among them the low-lying absorption $\beta$ which has the same value 0.25 eV in both compounds, and is caused by the Rashba spin splitting of the conduction band. An additional weak transition is found in BiTeCl, caused by the lower crystal symmetry.