We report on nanosecond-long, gate-dependent valley lifetimes of free charge carriers in monolayer WSe2, 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 WSe2 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).

中文翻译：

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揭露单层WSe2中免费载流子的山谷寿命。

我们报告了单层WSe2中自由电荷载流子的纳秒级长，与栅极有关的谷寿命，这是通过时间分辨的Kerr旋转和电迁移测量的组合明确确定的。当将费米能级调整到导带或价带时，谷底极化增加，但相应的谷底寿命却大大降低，这与电子声子散射和自旋轨道散射都一致。在带隙区域中，自旋极化的束缚激子的寿命最长。我们通过两个不同的，费米能级相关的散射通道（通过暗态或束缚态）对光激发的，谷极化的明亮三子进行了解释，以解释我们的发现。