Robustness against Disorder of Relativistic Spectral Properties in Chalcogenide Alloys

TL;DR

This paper introduces a new theoretical approach combining density-functional theory and the Coherent Potential Approximation to study disorder effects in chalcogenide alloys, revealing their spectral robustness near the Fermi energy and implications for topological properties.

Contribution

The study develops a novel method to analyze the interplay of disorder and spin-orbit coupling in IV-VI alloys, demonstrating spectral feature robustness and topological transition protection.

Findings

Spectral features near the Fermi energy are robust against substitutional disorder.

Disorder self-energy is negligible near the band gap, enabling observable Rashba-like spin splitting.

Band-character inversion related to topological transitions is protected in certain alloys.

Abstract

In order to carefully address the interplay between substitutional disorder and spin-orbit-coupling in IV-VI alloys, we propose a novel theoretical approach that integrates the reliability of plane-wave based density-functional theory beyond the local-density approximation with the Coherent Potential Approximation. By applying the proposed method to ternary chalcogenide alloys, we predict a substantial robustness of spectral features close to the Fermi energy against substitutional disorder. Supplementing our first-principles calculations with the analysis of the $k \cdot p$ model for rock-salt chalcogenides, we show that the disorder self-energy is vanishingly small close to the band gap, thus allowing for bulk Rashba-like spin splitting to be observed in ferroelectric alloys, such as PbS$_x$Te$_{1-x}$, and protecting the band-character inversion related to the topological transition in the recently discovered Topological Crystalline Insulator Pb$_{1-x}$Sn$_x$Te.