Excitation-induced transition to indirect band gaps in atomically thin transition metal dichalcogenide semiconductors

Abstract

Monolayers of transition metal dichalcogenides (TMDCs) exhibit an exceptionally strong Coulomb interaction between charge carriers due to the two-dimensional carrier confinement in connection with weak dielectric screening. High densities of excited charge carriers in the various band-structure valleys cause strong many-body renormalizations that influence both the electronic properties and the optical response of the material. We investigate electronic and optical properties of the typical monolayer TMDCs MoS${}_2$, MoSe${}_2$, WS${}_2$ and WSe${}_2$ in the presence of excited carriers by solving semiconductor Bloch equations on the full Brillouin zone. With increasing carrier density, we systematically find a reduction of the exciton binding energies due to Coulomb screening and Pauli blocking. Together with excitation-induced band-gap shrinkage this leads to redshifts of excitonic resonances up to the dissociation of excitons. As a central result, we predict for all investigated monolayer TMDCs that the $\Sigma$-valley shifts stronger than the K-valley. Two of the materials undergo a transition from direct to indirect band gaps under carrier excitation similar to well-known strain-induced effects. Our findings have strong implications for the filling of conduction-band valleys with excited carriers and are relevant to transport and optical applications as well as the emergence of phonon-driven superconductivity.

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• Momentum-resolved observation of exciton formation dynamics in monolayer WS${}_2$
• Exciton-Scattering-Induced Dephasing in Two-Dimensional Semiconductors
• Direct determination of momentum resolved electron transfer in the photo-excited MoS2/WS2 van der Waals heterobilayer by TR-ARPES
• Prospects and limitations of transition-metal dichalcogenide laser gain materials
• Bandgap Control in Two-Dimensional Semiconductors via Coherent Doping of Plasmonic Hot Electrons
• Microscopic origin of anomalous interlayer exciton transport in van der Waals heterostructures
• Ultrafast band-gap renormalization and build-up of optical gain in monolayer MoTe${}_2$
• Exciton-exciton interactions in van der Waals heterobilayers
• Electronic and Optical properties of transition metal dichalcogenides under symmetric and asymmetric field-effect doping
• Comprehensive tunneling spectroscopy of quasi-freestanding MoS${}_2$ on graphene on Ir(111)
• Excitonic Complexes and Emerging Interlayer Electron-Phonon Coupling in BN Encapsulated Monolayer Semiconductor Alloy: WS0.6Se1.4
• Phonon-assisted Exciton Dissociation in Transition Metal Dichalcogenides
• Excitonic theory of doping-dependent optical response in atomically thin semiconductors
• On the importance of electron-electron and electron-phonon scatterings and energy renormalizations during carrier relaxation in monolayer transition-metal dichalcogenides
• k-resolved ultrafast light-induced band renormalization in monolayer WS${}_2$ on graphene
• Persistence of charge ordering instability to Coulomb engineering in the excitonic insulator candidate TiSe${}_2$
• Doping-induced non-Markovian interference causes excitonic linewidth broadening in monolayer WSe${}_2$
• In-Gap Band Formation in a Periodically Driven Charge Density Wave Insulator
• Wannier-Function-Based Approach to Coupled Exciton-Phonon-Photon Dynamics in Two-Dimensional Semiconductors
• Reversible engineering the spin-orbit coupling of monolayer MoS2 via laser irradiation under controlled gas atmospheres