Manipulation of nonlinear optical responses in layered ferroelectric niobium oxide dihalides
Liangting Ye, Wenju Zhou, Dajian Huang, Xiao Jiang, Qiangbing Guo, Xinyu Cao, Shaohua Yan, Xinyu Wang, Donghan Jia, Dequan Jiang, Yonggang Wang, Xiaoqiang Wu, Xiao Zhang, Yang Li, Hechang Lei, Huiyang Gou, Bing Huang
Abstract
Abstract Realization of highly tunable second-order nonlinear optical responses, e.g., second-harmonic generation and bulk photovoltaic effect, is critical for developing modern optical and optoelectronic devices. Recently, the van der Waals niobium oxide dihalides are discovered to exhibit unusually large second-harmonic generation. However, the physical origin and possible tunability of nonlinear optical responses in these materials remain to be unclear. In this article, we reveal that the large second-harmonic generation in NbO X 2 ( X = Cl, Br, and I) may be partially contributed by the large band nesting effect in different Brillouin zone. Interestingly, the NbOCl 2 can exhibit dramatically different strain-dependent bulk photovoltaic effect under different polarized light, originating from the light-polarization-dependent orbital transitions. Importantly, we achieve a reversible ferroelectric-to-antiferroelectric phase transition in NbOCl 2 and a reversible ferroelectric-to-paraelectric phase transition in NbOI 2 under a certain region of external pressure, accompanied by the greatly tunable nonlinear optical responses but with different microscopic mechanisms. Our study establishes the interesting external-field tunability of NbO X 2 for nonlinear optical device applications.