Deciphering the Intense Post-Gap Absorptions of Monolayer Transition Metal Dichalcogenides
arXiv:2104.00291
Abstract
Rich valleytronics and diverse defect-induced or interlayer pre-bandgap excitonics have been extensively studied in transition metal dichalcogenides (TMDCs), a system with fascinating optical physics. However, more intense high-energy absorption peaks (~ 3 eV) above the bandgaps used to be long ignored and their underlying physical origin remains to be unveiled. Here, we employ momentum resolved electron energy loss spectroscopy to measure the dispersive behaviors of the valley excitons and intense higher-energy peaks at finite momenta. Combined with accurate Bethe Salpeter equation calculations, non-band-nesting transitions at Q valley and at midpoint of KM are found to be responsible for the high-energy broad absorption peaks in tungsten dichalcogenides and present spin polarizations similar to A excitons, in contrast with the band-nesting mechanism in molybdenum dichalcogenides. Our experiment-theory joint research will offer insights into the physical origins and manipulation of the intense high-energy excitons in TMDCs-based optoelectronic devices.
References in corpus (4)
- Valley polarization in MoS2 monolayers by optical pumping
- Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
- Observation of Moiré Excitons in WSe2/WS2 Heterostructure Superlattices
- k.p theory for two-dimensional transition metal dichalcogenide semiconductors