Valley Phenomena in the Candidate Phase Change Material WSe2(1-x)Te2x
Sean M. Oliver, Joshua Young, Sergiy Krylyuk, Thomas L. Reinecke, Albert Davydov, Patrick M. Vora
Alloyed transition metals dichalcogenides (TMDs) provide the unique opportunity for coupling band engineering and valleytronic phenomena in an atomically-thin platform. However, valley properties remain largely unexplored in TMD alloys. Here, we investigate the impact of alloying on the valley degree of freedom in monolayers of the phase change candidate material WSe2(1- x)Te2x. Low-temperature Raman and temperature-dependent photoluminescence measurements are used to examine the alloy-induced transition from the semiconducting 1H phase of WSe2 to the semimetallic 1Td phase of WTe2. These measurements reveal vibrational modes from 1H-WTe2 predicted with density functional theory calculations and indicate the effects of significant alloy disorder in the lattice due to the large Te bond lengths that introduce new defect states. Interestingly, valley polarization and coherence properties survive for substantial doping levels, and we find that alloys can sustain both valley polarization and coherence at higher temperatures than pure WSe2. These findings demonstrate the potential for optimizing semiconducting TMDs for valleytronic and phase change memory applications.