Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2

Simon Raiber, Paulo E. Faria Junior, Dennis Falter, Simon Feldl, Petter Marzena, Kenji Watanabe, Takashi Taniguchi, Jaroslav Fabian and Christian Schüller ()
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Simon Raiber: Institut für Experimentelle und Angewandte Physik, Universität Regensburg
Paulo E. Faria Junior: Institut für Theoretische Physik, Universität Regensburg
Dennis Falter: Institut für Experimentelle und Angewandte Physik, Universität Regensburg
Simon Feldl: Institut für Experimentelle und Angewandte Physik, Universität Regensburg
Petter Marzena: Institut für Experimentelle und Angewandte Physik, Universität Regensburg
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Jaroslav Fabian: Institut für Theoretische Physik, Universität Regensburg
Christian Schüller: Institut für Experimentelle und Angewandte Physik, Universität Regensburg

Nature Communications, 2022, vol. 13, issue 1, 1-8

Abstract: Abstract Layered van-der-Waals materials with hexagonal symmetry offer an extra degree of freedom to their electrons, the so-called valley index or valley pseudospin, which behaves conceptually like the electron spin. Here, we present investigations of excitonic transitions in mono- and multilayer WSe2 and MoSe2 materials by time-resolved Faraday ellipticity (TRFE) with in-plane magnetic fields, B∥, of up to 9 T. In monolayer samples, the measured TRFE time traces are almost independent of B∥, which confirms a close to zero in-plane exciton g factor g∥, consistent with first-principles calculations. In contrast, we observe pronounced temporal oscillations in multilayer samples for B∥ > 0. Our first-principles calculations confirm the presence of a non-zero g∥ for the multilayer samples. We propose that the oscillatory TRFE signal in the multilayer samples is caused by pseudospin quantum beats of excitons, which is a manifestation of spin- and pseudospin layer locking in the multilayer samples.

Date: 2022
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DOI: 10.1038/s41467-022-32534-3

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