Deciphering the Intense Postgap Absorptions of Monolayer Transition Metal Dichalcogenides

Author(s)
Jinhua Hong, Masanori Koshino, Ryosuke Senga, Thomas Pichler, Hua Xu, Kazu Suenaga
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 (similar to 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 BetheSalpeter equation calculations, non-band-nesting transitions at the Q valley and at the 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 TMDC-based optoelectronic devices.

Organisation(s)
Electronic Properties of Materials
External organisation(s)
National Institute of Advanced Industrial Science and Technology (AIST), Osaka University, Shaanxi Normal University
Journal
ACS Nano
Volume
15
Pages
7783-7789
No. of pages
7
ISSN
1936-0851
DOI
https://doi.org/10.1021/acsnano.1c01868
Publication date
04-2021
Peer reviewed
Yes
Austrian Fields of Science 2012
103018 Materials physics
Keywords
Portal url
https://ucris.univie.ac.at/portal/en/publications/deciphering-the-intense-postgap-absorptions-of-monolayer-transition-metal-dichalcogenides(a922a627-59bc-42f3-9aeb-8569809a9ce1).html