Origins of strong and/or quantized nonlinear optical responses in Weyl semimetals

Weyl semimetals and other topological materials can support unique electromagnetic responses different from ordinary matter. This talk starts with a brief review of the theory of linear and nonlinear optics in crystals, including recent work on how geometric properties of Bloch states such as the Berry curvature can lead to simplified expressions and sum rules. Previous results show that in Weyl semimetals, nonlinear optics is likely to be a more fruitful ground for novel behavior than linear response. In addition to the Weyl semimetal TaAs whose nonlinear optical properties are the subject of intense study, we explain how other Weyl materials lacking mirror symmetry (and certain related compounds) should have an approximately quantized circular photogalvanic effect (CPGE) and discuss the status of experimental searches for this effect in various materials.


The main results described were obtained in collaborative works with F. de Juan, B. M. Fregoso, A. G. Grushin, T. Morimoto, J. W. Orenstein, and D. Parker.