Physics and Materials Science Research Unit, University of Luxembourg , 162a avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg.
Institute of Materials Science (ICMUV), University of Valencia , Catedrático Beltrán 2, E-46980 Valencia, Spain.
Nano Lett. 2017 Aug 9;17(8):4549-4555. doi: 10.1021/acs.nanolett.7b00175. Epub 2017 Jul 14.
In single-layer WSe, a paradigmatic semiconducting transition metal dichalcogenide, a circularly polarized laser field can selectively excite electronic transitions in one of the inequivalent K valleys. Such selective valley population corresponds to a pseudospin polarization. This can be used as a degree of freedom in a "valleytronic" device provided that the time scale for its depolarization is sufficiently large. Yet, the mechanism behind the valley depolarization still remains heavily debated. Recent time-dependent Kerr experiments have provided an accurate way to visualize the valley dynamics by measuring the rotation of a linearly polarized probe pulse applied after a circularly polarized pump pulse. We present here a clear, accurate and parameter-free description of the valley dynamics. By using an atomistic, ab initio approach, we fully disclose the elemental mechanisms that dictate the depolarization effects. Our results are in excellent agreement with recent time-dependent Kerr experiments. We explain the Kerr dynamics and its temperature dependence in terms of electron-phonon-mediated processes that induce spin-flip intervalley transitions.
在单层 WSe2 中，一种典型的半导体过渡金属二卤族化合物，圆偏振激光场可以选择性地激发两个不等价 K 谷中的一个中的电子跃迁。这种选择性的谷填充对应于赝自旋极化。如果其去极化的时间尺度足够大，这可以作为“谷电子学”器件中的一个自由度。然而，谷去极化的机制仍然存在很大争议。最近的时间相关克尔实验通过测量圆偏振泵浦脉冲后施加的线性偏振探测脉冲的旋转，提供了一种准确可视化谷动力学的方法。我们在这里提供了一种清晰、准确且无参数的谷动力学描述。通过使用原子、从头算的方法，我们完全揭示了决定去极化效应的基本机制。我们的结果与最近的时间相关克尔实验非常吻合。我们根据电子-声子介导的过程来解释克尔动力学及其对温度的依赖性，这些过程会诱导自旋翻转谷间跃迁。
