论文标题
间接过渡对WS $ _2 $和WSE $ _2 $中谷极化的影响
Impact of indirect transitions on valley polarization in WS$_2$ and WSe$_2$
论文作者
论文摘要
控制半导体中载体的动量（称为山谷极化）是光电和信息技术的新资源。基于山谷的设备需要表现出高极化的材料。几层ws $ _2 $即使在室温下，也显示出惊人的旋转 - 瓦利极化超过90％。与之形成鲜明对比的是，尽管有预期的材料相似性，但几层WSE $ _2 $缺席两极分化。在这里，我们根据两个间接光学转变之间的相互作用来解释两种材料中谷地极化的起源。我们表明，导带中的$λ$ - k-valleys的相对能量最小值决定了直接k-k转变的自旋 - 瓦利极化。偏振出现时，随着K-Valley的能量升高到$λ$ -VALLEY以上，这是温度和层数的函数。我们的结果可以提高对WS $ _2 $中高自旋谷极化的理解。这种见解将影响在室温下运行的被动和可调valleytronic设备的设计。
Controlling the momentum of carriers in semiconductors, known as valley polarization, is a new resource for optoelectronics and information technologies. Materials exhibiting high polarization are needed for valley-based devices. Few-layer WS$_2$ shows a remarkable spin-valley polarization above 90%, even at room temperature. In stark contrast, polarization is absent for few-layer WSe$_2$ despite the expected material similarities. Here, we explain the origin of valley polarization in both materials based on the interplay between two indirect optical transitions. We show that the relative energy minima at the $Λ$- and K-valleys in the conduction band determine the spin-valley polarization of the direct K-K transition. Polarization appears as the energy of the K-valley rises above the $Λ$-valley as a function of temperature and number of layers. Our results advance the understanding of the high spin-valley polarization in WS$_2$. This insight will impact the design of both passive and tunable valleytronic devices operating at room temperature.
