Anomalous Hall transport by optically injected isospin degree of freedom in Dirac semimetal thin film

TL;DR

This study demonstrates that circularly polarized light can inject isospin polarization in Dirac semimetal thin films, leading to observable anomalous Hall effects, with potential applications in future information technology.

Contribution

It introduces a method to optically inject and detect isospin polarization in Dirac semimetals, revealing long-lived and reversible isospin dynamics.

Findings

Optical injection of isospin polarization using circularly polarized light.

Detection of anomalous Hall conductivity via terahertz Faraday rotation spectroscopy.

Observation of long scattering and decay times indicating robust isospin states.

Abstract

Chirality of massless fermions emergent in condensed matter is a key to understand their characteristic behavior as well as to exploit their functionality. However, chiral nature of massless fermions in Dirac semimetals has remained elusive, due to equivalent occupation of carriers with the opposite chirality in thermal equilibrium. Here, we show that the isospin degree of freedom, which labels the chirality of massless carriers from a crystallographic point of view, can be injected by circularly polarized light. Terahertz Faraday rotation spectroscopy successfully detects the anomalous Hall conductivity by a light-induced isospin polarization in a three-dimensional Dirac semimetal, Cd$_3$As$_2$. Spectral analysis of the Hall conductivity reveals a long scattering time and a long decay time, which are characteristic of the isospin. The long-lived, robust, and reversible character of the isospin promises potential application of Dirac semimetals in future information technology.