Non-uniform carrier density in Cd$_3$As$_2$ evidenced by optical spectroscopy

TL;DR

This study reveals significant spatial fluctuations in carrier density within Cd$_3$As$_2$ crystals, affecting their optical properties and influenced by sample treatment and crystal twinning, with implications for understanding their electronic behavior.

Contribution

It provides detailed optical characterization of Cd$_3$As$_2$ across various conditions, highlighting intrinsic carrier density fluctuations and their dependence on sample preparation.

Findings

Carrier density fluctuations up to 30% observed.

Fluctuations become more pronounced at low temperatures.

Mechanical treatment increases scattering rates and alters optical response.

Abstract

We report the detailed optical properties of Cd$_3$As$_2$ crystals in a wide parameter space: temperature, magnetic field, carrier concentration and crystal orientation. We investigate high-quality crystals synthesized by three different techniques. In all the studied samples, independently of how they were prepared and how they were treated before the optical experiments, our data indicate conspicuous fluctuations in the carrier density (up to 30%). These charge puddles have a characteristic scale of 100 $\mu$m, they become more pronounced at low temperatures, and possibly, they become enhanced by the presence of crystal twinning. The Drude response is characterized by very small scattering rates ($\sim 1$ meV) for as-grown samples. Mechanical treatment, such as cutting or polishing, influences the optical properties of single crystals, by increasing the Drude scattering rate and also modifying the high frequency optical response. Magneto-reflectivity and Kerr rotation are consistent with electron-like charge carriers and a spatially non-uniform carrier density.