Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe<sub>2</sub>.
Faria Junior, Paulo E
Ziegler, Jonas D
Qiu, Diana Y
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Lin, K., Ong, C. S., Bange, S., Faria Junior, P. E., Peng, B., Ziegler, J. D., Zipfel, J., et al. (2021). Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe<sub>2</sub>.. Nature communications, 12 (1) https://doi.org/10.1038/s41467-021-25499-2
Monolayer transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. Here, we report the existence of a new excitonic species, the high-lying exciton (HX), in single-layer WSe<sub>2</sub> with an energy of ~3.4 eV, almost twice the band-edge A-exciton energy, with a linewidth as narrow as 5.8 meV. The HX is populated through momentum-selective optical excitation in the K-valleys and is identified in upconverted photoluminescence (UPL) in the UV spectral region. Strong electron-phonon coupling results in a cascaded phonon progression with equidistant peaks in the luminescence spectrum, resolvable to ninth order. Ab initio GW-BSE calculations with full electron-hole correlations explain HX formation and unmask the admixture of upper conduction-band states to this complex many-body excitation. These calculations suggest that the HX is comprised of electrons of negative mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalizes the excitonic quantum-interference phenomenon recently discovered in optical second-harmonic generation (SHG) and explains the efficient Auger-like annihilation of band-edge excitons.
Deutsche Forschungsgemeinschaft (314695032)
Deutsche Forschungsgemeinschaft (German Research Foundation) (314695032)
External DOI: https://doi.org/10.1038/s41467-021-25499-2
This record's URL: https://www.repository.cam.ac.uk/handle/1810/329656
Attribution 4.0 International
Licence URL: https://creativecommons.org/licenses/by/4.0/