Quantum Geometric Origin of Strain-Tunable Giant Second-Harmonic Generation in Bi$_2$O$_2$X (X=S, Se, Te)

Zhefeng Lou; Zhihao Gong; Ziye Zhu; Wenbin Li; Xiao Lin; Hua Wang

paper

Quantum Geometric Origin of Strain-Tunable Giant Second-Harmonic Generation in Bi $_{2}$ O $_{2}$ X (X=S, Se, Te)

arXiv:2501.16741

Abstract

Two-dimensional (2D) materials with giant nonlinear optical (NLO) responses are essential for the development of advanced on-chip NLO devices. Using first-principles calculations, we predict a remarkable strain-induced enhancement of second-harmonic generation (SHG) in the high-performance 2D semiconductors Bi $_{2}$ O $_{2}$ X (X = S, Se, Te). The SHG susceptibilities of Bi $_{2}$ O $_{2}$ X under strain are on the order of 1~nm/V, rivalling the highest values reported among 2D materials. This giant SHG response originates from gauge-invariant geometric quantities, including the quantum metric, shift vector, and triple phase product. The strain also induces a bandgap variation in Bi $_{2}$ O $_{2}$ X. Intriguingly, in Bi $_{2}$ O $_{2}$ Te, strain-induced bandgap tuning drives a transition from a semiconductor to a half-metal, and ultimately to a polar metal. Our findings present a unique platform that combines strain-tunable bandgap engineering with exceptional NLO properties, while also highlighting the crucial role of quantum geometry in enhancing SHG.

8 pages, 4 figures

Quantum Geometric Origin of Strain-Tunable Giant Second-Harmonic Generation in Bi2​O2​X (X=S, Se, Te)

Abstract

Quantum Geometric Origin of Strain-Tunable Giant Second-Harmonic Generation in Bi $_{2}$ O $_{2}$ X (X=S, Se, Te)