Prof. Liang Wu
Department of Physics and Astronomy University of Pennsylvania
The second-order optical nonlinearity σ(2)(ω) has been a focus of basic research and technological development for decades as it is both a probe of inversion symmetry breaking in media and the basis for generating coherent light from far-infrared to ultraviolet wavelengths. Here, we focus on the relation between band geometry and nonlinear optics. We measured second harmonic generation (SHG) with incident photon energy from 0.4 eV - 1.6 eV on a polar semimetal TaAs with a sharp resonant peak detected at 0.7 eV, that is larger than previously measured in any crystal. Our discovery of a giant anisotropic σ(2)(ω) in TaAs raises the following questions: what is special about TaAs and/or polar metals that accounts for large resonant optical nonlinearity, and, is there a fundamental upper bound on σ(2)(ω) in such inversion breaking crystals? I will describe in the Rice-Mele model based on the band-geometric theory of nonlinear optical response that addresses these questions.
Prof. Liang Wu got his B.S. in Physics from Nanjing University in 2010 and Ph.D in Physics at Johns Hopkins University in 2015. He was a postdoc fellow in Physics at University of California, Berkeley from 2016 to 2018 before joining the department of Physics and Astronomy at the University of Pennsylvania in July 2018. He has been using terahertz spectroscopy and ultrafast optics to study topological insulators, Weyl semimetals and quantum spin liquids. He got the Richard L. Greene Dissertation Award in Experimental Condensed Matte Physics by the American Physical Society (2017) and the Michelson Postdoctoral Prize Lectureship by Case Western Reserve University (2017). He was selected as "30 under 30" in Science by Forbes Magazine in 2018.