Liang Wu


Band geometry and nonlinear optical studies on Weyl semimetals

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, 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 a simple model based on the band-geometric theory of nonlinear optical response that addresses these questions.