Excitons versus electron-hole plasma in monolayer transition metal dichalcogenide semiconductors

Abstract

When electron-hole pairs are excited in a semiconductor, it is a priori not clear if they form a fermionic plasma of unbound particles or a bosonic exciton gas. Usually, the exciton phase is associated with low temperatures. In atomically thin transition metal dichalcogenide semiconductors, excitons are particularly important even at room temperature due to strong Coulomb interaction and a large exciton density of states. Using state-of-the-art many-body theory including dynamical screening, we show that the exciton-to-plasma ratio can be efficiently tuned by dielectric substrate screening as well as charge carrier doping. Moreover, we predict a Mott transition from the exciton-dominated regime to a fully ionized electron-hole plasma at excitation densities between $3\times 10^{12}$ cm${}^{-2}$ and $1\times 10^{13}$ cm${}^{-2}$ depending on temperature, carrier doping and dielectric environment. We propose the observation of these effects by studying excitonic satellites in photoemission spectroscopy and scanning tunneling microscopy.

References in corpus (4)

• Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
• Scanning tunneling spectroscopy of high-temperature superconductors
• High-temperature superfluidity with indirect excitons in van der Waals heterostructures
• Spin and Valley Control of Free Carriers in Single-Layer WS${}_2$

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• Theory of the Coherent Response of Magneto-Excitons and Magneto-Biexcitons in Monolayer Transition Metal Dichalcogenides
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• Microscopic Theory of Exciton-Exciton Annihilation in Two-Dimensional Semiconductors
• Variational and field-theoretical approach to exciton-exciton interactions and biexcitons in semiconductors
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• Valley-controlled many-body exciton interactions in monolayer WSe${}_2$ phototransistors