Sliding Ferroelectricity and Nonlinear Light-Matter Interaction in 2D Quantum Materials

The ability to achieve noninvasive detection and efficient control of electric and magnetic orders as well as topology in 2D quantum materials is of great importance to the development of ultrathin quantum devices. In this talk, I will present our theoretical effort on understanding and predicting the sliding ferroelectricity and nonlinear response/memory effect in 2D quantum materials. I will first discuss sliding ferroelectricity in time-reversal invariant few-layer T_d-WTe₂. Although semimetallic it holds out-of-plane polarization which can be switched via interlayer sliding under vertical electric field. Moreover, ferroelectric nonlinear Hall effect can be achieved in few-layer WTe₂ by utilizing the intrinsic coupling among nonlinear susceptibility, crystalline symmetry, and quantum geometry of electronic states, paving a theoretical foundation for nonlinear quantum memory such as Berry curvature memory. Recent experimental demonstration of ferroelectric nonlinear Hall effect and Berry curvature memory in few-layer WTe₂ will also be discussed. Next, I will present our recent study of nonlinear photocurrent in PT-symmetric magnetic topological quantum materials where nonlinear probe could be particularly fruitful for probing and understanding magnetic topological quantum materials. Finally, I will briefly introduce our recently-developed unified quantum geometric approach based on generalized Wilson loop representation for computing general physical responses.