Work

High-temperature observation of intralayer, interlayer, and Rydberg excitons in bulk van der Waals alloy single crystals

Year: 2024

Type: article

Abstract: Transition metal dichalcogenides exhibit remarkable optical properties due to the diverse number of strongly bound excitons, which can be fine-tuned by alloying. Despite a flurry of research activity in characterizing these excitons, a comprehensive and profound understanding of their behavior with temperature is lacking. Here, we report the rich spectrum of excitonic features within bulk van der Waals alloy ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{S}}_{2}$ and ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{Se}}_{2}$ single crystals through temperature-dependent reflectance spectroscopy and first-principles calculations. We observed Rydberg excitons and interlayer excitons in both the single crystals. Notably, we provide the first experimental evidence of highly energetic ${\mathrm{A}}^{\ensuremath{'}}$ and ${\mathrm{B}}^{\ensuremath{'}}$ excitons in ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{S}}_{2}$ at room temperature. The strong carrier-phonon scattering significantly broadens the ${\mathrm{A}}^{\ensuremath{'}}, {\mathrm{B}}^{\ensuremath{'}}$, and interlayer excitons at room temperature in bulk ${\mathrm{Mo}}_{0.5}{\mathrm{W}}_{0.5}{\mathrm{S}}_{2}$ single crystal compared to its selenide. Our findings, supported by density functional theory and Bethe-Salpeter equation calculations, signify the crucial role of carrier-phonon interactions. These results open pathways for next-generation optoelectronic devices and quantum technologies operating at high temperature.

Source: Physical review. B./Physical review. B

DOI: 10.1103/physrevb.110.075205