First-Principles Theory of Nonlinear Optical Responses in 2D Semiconductors and Topological Materials*

Giant nonlinear optical responses were recently observed in 2D semiconductors and topological materials. Understanding their microscopic origin thus becomes important for both fundamentals of nonlinear optics and development of technological applications. Here I will report our recent first-principles theoretical development towards unveiling the electronic structure origin of their nonlinear optical responses, including (a) second harmonic generation [1] and nonlinear photocurrent [2] in 2D noncentrosymmetric materials and (b) nonlinear ferroelectric photocurrent in topological materials [3]. I will also discuss microscopic relations between nonlinear responses and topological quantities such as shift vector, Berry curvature dipole, etc. Our findings suggest the possibility to achieve deep understanding of nonlinear optical responses in 2D and topological materials using first-principles approaches. References: [1] H Wang and X Qian. Nano Letters 17, 5027-5034 (2017). [2] H Wang and X Qian. Quantum Nonlinear Ferroic Optical Hall Effect. submitted (2018). [3] H Wang and X Qian. Nonlinear Ferroelectric Photocurrent in Topological Materials. in preparation (2018).