Giant intrinsic anomalous terahertz Faraday rotation in the magnetic Weyl semimetal Co${}_2$MnGa at room temperature

Abstract

We report measurement of terahertz anomalous Hall conductivity and Faraday rotation in the magnetic Weyl semimetal Co${}_2$MnGa thin films as a function of the magnetic field, temperature and thickness, using time-domain terahertz spectroscopy. The terahertz conductivity shows a thickness-independent anomalous Hall conductivity of around 600 $\hat{I}{\text{c◯}}^{-1}\cdot c{m}^{-1}$ at room temperature, and it is also frequency-independent from 0.2-1.5 THz. The magnitude of the longitudinal and Hall conductivities, the weak spin-orbit coupling, and the very close positioning of Weyl points to the chemical potential all satisfy the criteria for intrinsic anomalous Hall conductivity. First-principle calculation also supports the frequency-independent intrinsic anomalous Hall conductivity at low frequency. We also find a thickness-independent Faraday rotation of 59 ($\pm 6$) mrad at room temperature, which comes from the intrinsic Berry curvature contribution. In the thinnest 20 nm sample, the Faraday rotation divided by the sample thickness reaches around 3 mrad/nm due to Berry curvature, and is the largest reported at room temperature. The giant Verdet constant of the order of 10 ${}^6$ rad m ${}^{-1}$ T ${}^{-1}$ at room temperature and the large Hall angle around 8.5 $\%$ from 0.2-1.5 THz indicates that Co${}_2$MnGa is promising for THz spintronics at room temperature.

Accepted, Phys. Rev. B