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

TL;DR

This study demonstrates giant, intrinsic anomalous Faraday rotation and Hall conductivity in Co$_2$MnGa thin films at room temperature, highlighting their potential for terahertz spintronic applications due to frequency-independent and thickness-independent properties.

Contribution

It provides the first experimental observation of large, intrinsic, and frequency-independent anomalous Hall conductivity and Faraday rotation in a magnetic Weyl semimetal at room temperature.

Findings

Thickness-independent anomalous Hall conductivity of ~600 Ω^{-1}·cm^{-1} at room temperature.

Record-high Faraday rotation of 59 mrad at room temperature, largest reported.

Giant Verdet constant (~10^6 rad m^{-1} T^{-1}) indicating potential for THz spintronics.

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 $\Omega^{-1}\cdot cm^{-1}$ 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 ($\pm6$) 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.