Valley Phenomena in the Candidate Phase Change Material WSe$_{2(1-x)}$Te$_{2x}$

TL;DR

This study explores valley phenomena in monolayer WSe$_{2(1-x)}$Te$_{2x}$ alloys, revealing persistent valley polarization and coherence despite alloy disorder, and demonstrates potential for band engineering in valleytronic applications.

Contribution

It provides the first detailed investigation of valley properties in WSe$_{2(1-x)}$Te$_{2x}$ alloys, combining experimental and theoretical analysis to show robustness of valley features.

Findings

Valley polarization persists at high Te compositions.

Alloy disorder affects low-energy emission features.

Valley coherence is more temperature-robust in alloys.

Abstract

Alloyed transition metal dichalcogenides provide an opportunity for coupling band engineering with valleytronic phenomena in an atomically-thin platform. However, valley properties in alloys remain largely unexplored. We investigate the valley degree of freedom in monolayer alloys of the phase change candidate material WSe$_{2(1-x)}$Te$_{2x}$. Low temperature Raman measurements track the alloy-induced transition from the semiconducting 1H phase of WSe$_2$ to the semimetallic 1T$_d$ phase of WTe$_2$. We correlate these observations with density functional theory calculations and identify new Raman modes from W-Te vibrations in the 1H alloy phase. Photoluminescence measurements show ultra-low energy emission features that highlight alloy disorder arising from the large W-Te bond lengths. Interestingly, valley polarization and coherence in alloys survive at high Te compositions and are more robust against temperature than in WSe$_2$. These findings illustrate the persistence of valley properties in alloys with highly dissimilar parent compounds and suggest band engineering can be utilized for valleytronic devices.