Symmetry-breaking and spin-blockage effects on carrier dynamics in single-layer tungsten diselenide
Symmetry-breaking and spin-blockage effects on carrier dynamics in single-layer tungsten diselenide
复制标题
DOI：
10.1103/physrevb.100.214309
复制
发表时间：
2019-12-17
影响因子：
3.7
通讯作者：
Chiang, Tai-Chang
中科院分区：
文献类型：
--
作者：
Liu, Ro-Ya;Lin, Meng-Kai;Chiang, Tai-Chang
了解由脉冲光激发引发的材料中载流子的产生和演化是发展超快光电子学的核心。我们在这里证明，一个系统的动态响应可以大大修改时，其物理尺寸减小到原子尺度，设备小型化的最终限制。单层（SL）的钨二硒化物（WSe2）相对于散装WSe2的比较研究表明，时间和角度分辨光电子能谱（TRARPES）测量的瞬态响应的实质性差异。在散装WSe 2的导带最小值，填充光泵浦，迅速衰减。SL WSe 2的相应衰减要慢得多，并表现出两个时间常数。结果表明，在SL中存在两个不同的衰变通道，这与二维极限中空间反演对称性的破坏有关。这种对称性破缺提升了能带的自旋简并度，从而导致一个自旋通道的衰变受阻。单层和散装之间的鲜明对比说明了基本的载流子散射过程中，可以大大修改的尺寸和体积减少的影响，在不同的时间尺度上运行。
Understanding carrier creation and evolution in materials initiated by pulsed optical excitation is central to developing ultrafast optoelectronics. We demonstrate herein that the dynamic response of a system can be drastically modified when its physical dimension is reduced to the atomic scale, the ultimate limit of device miniaturization. A comparative study of single-layer (SL) tungsten diselenide (WSe2) relative to bulk WSe2 shows substantial differences in the transient response as measured by time- and angle-resolved photoemission spectroscopy (TRARPES). The conduction-band minimum in bulk WSe2, populated by optical pumping, decays promptly. The corresponding decay for SL WSe2 is much slower and exhibits two time constants. The results indicate the presence of two distinct decay channels in the SL that are correlated with the breaking of space inversion symmetry in the two-dimensional limit. This symmetry breaking lifts the spin degeneracy of the bands, which in turn causes the blockage of decay for one spin channel. The stark contrast between the single layer and the bulk illustrates the basic carrier scattering processes operating at different timescales that can be substantially modified by dimensional and symmetry-reduction effects.