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arXiv · 2007.14712

Valley lifetimes of conduction band electrons 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

One of the main tasks in the investigation of 2-dimensional transition metal dichalcogenides is the determination of valley lifetimes. In this work, we combine time-resolved Kerr rotation with electrical transport measurements to explore the gate-dependent valley lifetimes of free conduction band electrons of monolayer WSe$_2$. When tuning the Fermi energy into the conduction band we observe a strong decrease of the respective valley lifetimes which is consistent with both spin-orbit and electron-phonon scattering. We explain the formation of a valley polarization by the scattering of optically excited valley polarized bright trions into dark states by intervalley scattering. Furthermore, we show that the conventional time-resolved Kerr rotation measurement scheme has to be modified to account for photo-induced gate screening effects. Disregarding this adaptation can lead to erroneous conclusions drawn from gate-dependent optical measurements and can completely mask the true gate-dependent valley dynamics.

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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. 2020-07-29. Valley lifetimes of conduction band electrons in monolayer WSe$_2$. https://doi.org/10.1117/12.2567652

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