On the importance of electron-electron and electron-phonon scatterings and energy renormalizations during carrier relaxation in monolayer transition-metal dichalcogenides

Abstract

An $abinitio$ based fully microscopic many-body approach is used to study the carrier relaxation dynamics in monolayer transition-metal dichalcogenides. Bandstructures and wavefunctions as well as phonon energies and coupling matrix elements are calculated using density functional theory. The resulting dipole and Coulomb matrix elements are implemented in the Dirac-Bloch equations to calculate carrier-carrier and carrier-phonon scatterings throughout the whole Brillouin zone. It is shown that carrier scatterings lead to a relaxation into hot quasi-Fermi distributions on a single femtosecond timescale. Carrier cool down and inter-valley transitions are mediated by phonon scatterings on a picosecond timescale. Strong, density-dependent energy renormalizations are shown to be valley-dependent. For MoTe${}_2$, MoSe${}_2$ and MoS${}_2$ the change of energies with occupation is found to be about 50$\%$ stronger in the $\Sigma$ and $\Lambda$ side valleys than in the $K$ and $K^{\prime }$ valleys. However, for realistic carrier densities, the materials always maintain their direct bandgap at the $K$ points of the Brillouin zone.

10 pages, 8 figures

References in corpus (11)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Valley polarization in MoS2 monolayers by optical pumping
• Tightly bound excitons in monolayer WSe2
• Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Variation of the fundamental band gap nature in curved two-dimensional WS2
• Renormalization of quasiparticle band gap in doped two-dimensional materials from many-body calculations
• Hot-electron cooling by acoustic and optical phonons in monolayers of MoS${}_2$ and other transition-metal dichalcogenides
• Electronic Band Structure of Transition Metal Dichalcogenides from Ab Initio and Slater-Koster Tight-Binding Model
• Phonon-assisted inter-valley scattering determines ultrafast exciton dynamics in MoSe${}_2$ bilayers