Optical gyrotropy as a probe of the Berry curvature and intrinsic orbital moment on the Fermi surface

In crystals without a center of inversion, the Bloch states acquire a Berry curvature and an intrinsic orbital moment in momentum space. Out of the 21 noncentrosymmetric crystal classes, 18 are "gyrotropic" (optically active). In gyrotropic metals, the Berry curvature and intrinsic orbital moment on the Fermi surface can be probed by low-frequency optical experiments. The former gives rise to an intraband photocurrent induced by circularly-polarized light, and the latter to intraband natural optical rotation. I will begin this presentation by introducing the phenomenology and microscopic theory of these effects. As an application, I will discuss first-principles results for p-doped trigonal tellurium. We find that the experimentally observed sign reversal with temperature of the circular photocurrent can be explained by the presence of Weyl points near the bottom of the conduction band acting as sources and sinks of Berry curvature.