Gyrotropic effects in trigonal tellurium studied from first principles

TL;DR

This study uses first-principles calculations to analyze gyrotropic effects in p-doped trigonal tellurium, revealing how Berry curvature and orbital magnetic moments influence optical and magnetic responses, including sign reversals with temperature.

Contribution

It provides a detailed ab initio explanation of gyrotropic effects in tellurium, linking Weyl points and Berry curvature to observed optical phenomena and sign reversals.

Findings

Sign reversal of circular photogalvanic effect explained by Weyl points.

Current induces detectable optical rotation via Faraday effect.

Polarization plane rotates opposite to spiral chain bonds, matching recent experiments.

Abstract

We present a combined ab initio study of several gyrotropic effects in p-doped trigonal tellurium (effects that reverse direction with the handedness of the spiral chains in the atomic structure). The key ingredients in our study are the k-space Berry curvature and intrinsic orbital magnetic moment imparted on the Bloch states by the chirality of the crystal structure. We show that the observed sign reversal with temperature of the circular photogalvanic effect can be explained by the presence of Weyl points near the bottom of the conduction band acting as sources and sinks of Berry curvature. The passage of a current along the trigonal axis induces a rather small parallel magnetization, which can nevertheless be detected by optical means (Faraday rotation of transmitted light) due to the high transparency of the sample. In agreement with experiment, we find that when infrared light propagates antiparallel to the current at low doping the current-induced optical rotation enhances the natural optical rotation. According to our calculations the plane of polarization rotates in the opposite sense to the bonded atoms in the spiral chains, in agreement with a recent experiment that contradicts earlier reports.