Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 36: 2D Materials and their Heterostructures I (joint session DS/HL/O)
O 36.7: Talk
Tuesday, March 17, 2020, 11:00–11:15, CHE 89
Unveiling valley lifetimes of free charge carriers in monolayer WSe2 — •Manfred Ersfeld1, Frank Volmer1, Lars Rathmann1, Luca Kotewitz1, Maximilian Heithoff1, Mark Lohmann2, Bowen Yang3, Kenji Watanabe4, Takashi Taniguchi4, Ludwig Bartels3, Jing Shi2, Christoph Stampfer1, 5, and Bernd Beschoten1 — 12nd Institute of Physics and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany — 2Department of Physics and Astronomy, University of California, Riverside, California 92521, USA — 3Department of Chemistry and Materials Science & Engineering Program, University of California, Riverside, California 92521, USA — 4National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan — 5Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany
We report on nanosecond long, gate-dependent valley lifetimes of free charge carriers in WSe2, unambiguously identified by the combination of time-resolved Kerr rotation (TRKR) and electrical transport measurements. While the valley polarization increases when tuning the Fermi level into the conduction or valence band, there is a strong decrease of the respective valley lifetime consistent with both electron-phonon and spin-orbit scattering. The longest lifetimes are seen for spin-polarized bound excitons in the band gap region. We explain our findings via two distinct, Fermi level-dependent scattering channels of optically excited, valley polarized bright trions either via dark or bound states.