Circular dichroism as a probe for topology in three-dimensional semimetals

TL;DR

This paper proposes using circular dichroism in response to a periodic drive as a method to detect the topological properties of three-dimensional semimetals, linking the dichroic response to the ground-state Chern number.

Contribution

It introduces a novel approach to probe the topology of semimetals via circular dichroism, including analytical and numerical validation for various pseudospin systems.

Findings

Dichroic response is quantized above a critical frequency in isotropic systems.

Tilt does not affect the dichroic response, but anisotropy can disrupt quantization.

The method effectively infers the ground-state Chern number from the dichroic response.

Abstract

Higher-pseudospin fermions, associated with multiple band-crossings in topological semimetals, are the condensed matter analogues of higher-spin fermions in high-energy physics. In this paper, we demonstrate that analyzing the response of a circular drive is an effective way to detect the topology of the lowest-energy Bloch band, as it can be connected to a frequency-dependent probe. The dichroic response exhibits circular dichroism due to the differential excitation rates by the left- and right-circular orientations of a time-periodic drive, induced on a filled band, because of the geometrical properties of the Bloch bands. Our analytical approximation reveals that the dichroic response is quantized for isotropic systems, when the frequency of the drive is above a critical value, and thus correctly infers the ground-state Chern number. We demonstrate this through explicit numerical computations by considering three kinds of semimetals with pseudospin values of 1/2, 1, and 3/2, respectively, and all having linear dispersions. Furthermore, we investigate the effects of tilt and anisotropy on the systems, and find that although tilt does not have any effect on the response, the presence of anisotropy can drastically hamper the quantization. Our scheme thus provides an important methodology for designing future experiments to detect the topology of band structures.