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O: Fachverband Oberflächenphysik

O 36: 2D Materials and their Heterostructures I (joint session DS/HL/O)

O 36.7: Vortrag

Dienstag, 17. März 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 Stampfer^{1, 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.