Topological Phase Transition in 2D 1T′‐WSTe

Abstract

The topological phase transition between normal and topological insulators is essential in topological mechanism analysis and search for new topological materials. Herein, on the basis of the well‐known monolayer 2D topological insulator 1T′‐WTe2, a new 2D material 1T′‐WSTe is constructed. It is a typical central inversion asymmetric 2D topological insulator. The fascinating feature of this material is that its low‐energy electronic structure is very similar to the inversion broken topological phase transition point. The first‐principles calculations reveal that the ±4% uniaxial strain can effectively turn the 2D material into topological insulator or normal insulator phases.

Second Harmonic Generation Control in 2D Layered Materials: Status and Outlook

“…[33,331] In addition, 2DLMs are a huge family of materials and have encyclopaedic properties including ferroelectric, ferromagnetic, magnetoelectric, superconductive, topological, and CDW properties. [49,50,[52][53][54][55][419][420][421] For example, in topological Weyl semimetals, the divergence of Berry curvature near Weyl point can give rise to a stronger magnitude of the SHG, which is beneficial for the vigorous development of topological photonics. [420] Looking forward, the continuing development of new degrees of freedom and exotic physics phenomenons of 2DLMs will lay a solid foundation for the expansion of the construction of nextgeneration novel functional SHG devices.…”

Application of Second Harmonic Generation in Characterization of 2D Materials

“…Ge 晶粒存在晶界和晶粒取向后， 由于晶体生长过程 中相邻边缘的边界方向取决于相邻边缘的相对生长 速率 [45] ，根据两个晶粒接触并继续生长时形成的对 称倾斜边界，揭示了两个晶粒相似的边以相同的间 距合并，随后的边界将两条边平分，从而形成对称 的倾斜边界的生长机制。 directions of the two grains [24] 5 [47] 用两点弯曲法对 MoS2 施加不同的 单轴拉伸应变，通过光弹性张量建立起应变和非线 性磁化率之间的关系 [48] ，测量偏振分辨二次谐波信 号强度，通过三个偏振倍频测量点确定局部应变张 量，实现高效快速的应变场成像(图 7(d, e))，补充和 扩展了已有的光学应变测量方法，使用这种技术， 可以在亚皮秒时间尺度上表征瞬态晶体变形 [47] 。因 此，基于二次谐波对于应变的灵敏反应，二次谐波 强度可以作为一种直接、灵敏地监测应变幅度的手 段。 此外，随着材料缺陷的引入，材料的性能也能 够得以控制或调整 [49][50] [46] ; (d, e) Schematic illustration of two-point bending method and the SHG patterns for applied tensile strains of 0.1%, 0.5%, and 0.95% [47] 图 8 二次谐波表征二维材料的缺陷 Fig. 8 Characterization of the defects of 2D materials by SHG (a-c) the optical image, fluorescence image and second harmonic mapping image of monolayer WS2 [51] 6 二次谐波与拉曼光谱、 光致发光光谱 的多维度关联分析 [52] (f, i) Corresponding Raman spectra [52] [53][54][55] ，可以采用二次谐波 进一步研究磁有序结构、磁畴和超快磁动力学等 [55] 。 随着二维材料的相变引起了研究者广泛关注 [56][57] ， 未来也可以采用二次谐波对相变材料的结构转变进 行表征。 参考文献:…”