We use microscopic many-body models based on first principle density functional theory to investigate the high harmonic generation (HHG) in monolayer transition metal dichalcogenides (ML-TMDCs) at the example of MoS2. A two-dimensional bandstructure model is utilized that allows for the realistic inclusion of Coulomb correlations. It is shown that for off-resonant mid-IR excitation Coulomb correlations lead to a dramatic enhancement of HHG intensity by up to two orders of magnitude. For resonant excitation near the fundamental excitonic resonance the Coulomb interaction leads to dressed harmonics. These have a sub-floor of broad spectral contributions. The amplitude of these contributions is about four to six orders of magnitude below the peak. The width scales linearly with the exciting field and can reach hundreds of meV.
First principle DFT-based microscopic many-body models are used to investigate inter- and intra-valley carrier dynamics in the monolayer transition-metal dichalcogenide MoTe2. Electron-electron and electron-phonon scatterings are calculated for transitions within the full Brillouin zone to determine overall carrier relaxation timescales as well as intra- and inter-valley transition rates. For excitation above the barriers separating bandstructure valleys carriers are found to relax on a ten femtosecond timescale into hot quasi-Fermi distributions at the band minima. Subsequently, the hot carrier plasma is cooled down on a picosecond timescale predominantly through emission of optical phonons. Local carrier occupations lead to strong energy renormalizations in momentum space. However, for the material investigated here, the global energy minimum remains at the K-points once carriers relax into global quasi-Fermi distributions. No transition from a direct to an indirect bandgap is observed.
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