Ersfeld Manfred, Volmer Frank, Rathmann Lars, Kotewitz Luca, Heithoff Maximilian, Lohmann Mark, Yang Bowen, Watanabe Kenji, Taniguchi Takashi, Bartels Ludwig, Shi Jing, Stampfer Christoph, Beschoten Bernd
2nd Institute of Physics and JARA-FIT, RWTH Aachen University, Aachen 52074, Germany.
Department of Physics and Astronomy, University of California, Riverside, Riverside 92521, California, United States.
Nano Lett. 2020 May 13;20(5):3147-3154. doi: 10.1021/acs.nanolett.9b05138. Epub 2020 Mar 31.
We report on nanosecond-long, gate-dependent valley lifetimes of free charge carriers in monolayer WSe, 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 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).
我们报道了单层WSe₂中自由电荷载流子纳秒级、与栅极相关的谷寿命，通过时间分辨克尔旋转和电输运测量的结合明确识别。当将费米能级调至导带或价带时，谷极化增加，而相应的谷寿命大幅下降，这与电子 - 声子和自旋 - 轨道散射均相符。在带隙区域中自旋极化的束缚激子具有最长的寿命。我们通过光学激发的、谷极化的亮三重子经由暗态或束缚态的两种不同的、依赖费米能级的散射通道来解释我们的发现。通过静电栅控，我们证明过渡金属二硫属化物WSe₂可以被调谐为要么是长寿命局域自旋态的理想主体，要么允许自由电荷载流子具有纳秒级谷寿命（>10 ns）。
