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arXiv · 1911.11692

Unveiling valley lifetimes of free charge carriers in monolayer WSe$_2$

Manfred Ersfeld·Frank Volmer·Lars Rathmann·Luca Kotewitz·Maximilian Heithoff·Mark Lohmann·Bowen Yang·Kenji Watanabe·Takashi Taniguchi·Ludwig Bartels·Jing Shi·Christoph Stampfer·Bernd Beschoten
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Abstract

We report on nanosecond long, gate-dependent valley lifetimes of free charge carriers in monolayer WSe$_2$, unambiguously identified by the combination of time-resolved Kerr rotation 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. By electrostatic gating we demonstrate that the transition metal dichalcogenide WSe$_2$ can be tuned to be either an ideal host for long-lived localized spin states or allow for nanosecond valley lifetimes of free charge carriers (> 10 ns).

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Manfred Ersfeld, Frank Volmer, Lars Rathmann, Luca Kotewitz, Maximilian Heithoff, Mark Lohmann, Bowen Yang, Kenji Watanabe, Takashi Taniguchi, Ludwig Bartels, Jing Shi, Christoph Stampfer, Bernd Beschoten. 2020-02-06. Unveiling valley lifetimes of free charge carriers in monolayer WSe$_2$. https://doi.org/10.1021/acs.nanolett.9b05138

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