Regensburg 2022 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 20: 2D Materials 4 (joint session HL/CPP/DS)
HL 20.4: Talk
Wednesday, September 7, 2022, 10:15–10:30, H36
Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2 — •Simon Raiber1, Paulo E. Faria Junior2, Dennis Falter1, Simon Feldl1, Petter Marzena1, Kenji Watanabe3, Takashi Taniguchi4, Jaroslav Fabian2, and Christian Schüller1 — 1Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany — 2Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany — 3Research Center for Functional Materials, NIMS, Tsukuba, Japan — 4International Center for Materials Nanoarchitectonics, NIMS, Tsukuba, Japan
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, of up to B = 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, consistent with first-principles calculations. In stark contrast, we observe pronounced temporal oscillations in multilayer samples for B > 0. Remarkably, the extracted in-plane g factors are very close to reported out-of-plane exciton g factors of the materials, namely |g< 1s| = 3.1 +/- 0.2 and 2.5 +/- 0.2 for the 1s A excitons in WSe2 and MoSe2 multilayers, respectively. Our first-principles calculations nicely confirm the presence of a non-zero in-plane 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.