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Efficient phonon cascades in WSe2 monolayers.

Accepted version
Peer-reviewed

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Article

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Authors

Paradisanos, Ioannis  ORCID logo  https://orcid.org/0000-0001-8310-710X
Wang, Gang 
Cadore, Alisson R 

Abstract

Energy relaxation of photo-excited charge carriers is of significant fundamental interest and crucial for the performance of monolayer transition metal dichalcogenides in optoelectronics. The primary stages of carrier relaxation affect a plethora of subsequent physical mechanisms. Here we measure light scattering and emission in tungsten diselenide monolayers close to the laser excitation energy (down to ~0.6 meV). We reveal a series of periodic maxima in the hot photoluminescence intensity, stemming from energy states higher than the A-exciton state. We find a period ~15 meV for 7 peaks below (Stokes) and 5 peaks above (anti-Stokes) the laser excitation energy, with a strong temperature dependence. These are assigned to phonon cascades, whereby carriers undergo phonon-induced transitions between real states above the free-carrier gap with a probability of radiative recombination at each step. We infer that intermediate states in the conduction band at the Λ-valley of the Brillouin zone participate in the cascade process of tungsten diselenide monolayers. This provides a fundamental understanding of the first stages of carrier-phonon interaction, useful for optoelectronic applications of layered semiconductors.

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Keywords

cond-mat.mes-hall, cond-mat.mes-hall, cond-mat.mtrl-sci

Journal Title

Nat Commun

Conference Name

Journal ISSN

2041-1723
2041-1723

Volume Title

12

Publisher

Nature Research

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All rights reserved
Sponsorship
Engineering and Physical Sciences Research Council (EP/L016087/1)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (696656)
EPSRC (via University of Manchester) (R119256)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (785219)
European Research Council (842251)
Engineering and Physical Sciences Research Council (EP/G042357/1)
European Research Council (319277)
Engineering and Physical Sciences Research Council (EP/K01711X/1)
Engineering and Physical Sciences Research Council (EP/K017144/1)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (881603)