Tong Tong, Chen Ruijie, Ke Yuxuan, Wang Qian, Wang Xinchao, Sun Qinjun, Chen Jie, Gu Zhiyuan, Yu Ying, Wei Hongyan, Hao Yuying, Fan Xiaopeng, Zhang Qing
College of Electronic Information and Optical Engineering, Taiyuan University of Technology, Taiyuan 030024, China.
College of Physics, Taiyuan University of Technology, Taiyuan 030024, China.
ACS Nano. 2024 Aug 20;18(33):21939-21947. doi: 10.1021/acsnano.4c02807. Epub 2024 Aug 8.
In moiré crystals resulting from the stacking of twisted two-dimensional (2D) layered materials, a subtle adjustment in the twist angle surprisingly gives rise to a wide range of correlated optical and electrical properties. Herein, we report the synthesis of supertwisted WS spirals and the observation of giant second harmonic generation (SHG) in these spirals. Supertwisted WS spirals featuring different twist angles are synthesized on a Euclidean or step-edge particle-induced non-Euclidean surface using carefully designed water-assisted chemical vapor deposition. We observed an oscillatory dependence of SHG intensity on layer number, attributed to atomically phase-matched nonlinear dipoles within layers of supertwisted spiral crystals where inversion symmetry is restored. Through an investigation into the twist angle evolution of SHG intensity, we discovered that the stacking model between layers plays a crucial role in determining the nonlinearity, and the SHG signals in supertwisted spirals exhibit enhancements by a factor of 2 to 136 when compared with the SHG of the single-layer structure. These findings provide helpful perspectives on the rational growth of 2D twisted structures and the implementation of twist angle adjustable endowing them great potential for exploring strong coupling correlation physics and applications in the field of twistronics.
在由扭曲的二维（2D）层状材料堆叠而成的莫尔晶体中，扭转角的微小调整出人意料地产生了一系列相关的光学和电学性质。在此，我们报告了超扭曲WS螺旋的合成以及在这些螺旋中观察到的巨大二次谐波产生（SHG）。利用精心设计的水辅助化学气相沉积法，在欧几里得或台阶边缘粒子诱导的非欧几里得表面上合成了具有不同扭转角的超扭曲WS螺旋。我们观察到SHG强度对层数的振荡依赖性，这归因于超扭曲螺旋晶体层内原子级相位匹配的非线性偶极子，其中反演对称性得以恢复。通过对SHG强度的扭转角演化进行研究，我们发现层间堆叠模型在决定非线性方面起着关键作用，与单层结构的SHG相比，超扭曲螺旋中的SHG信号增强了2至136倍。这些发现为二维扭曲结构的合理生长以及扭转角可调的实现提供了有益的视角，赋予它们在探索强耦合相关物理和在扭曲电子学领域应用方面的巨大潜力。
