Giant intrinsic anomalous terahertz Faraday rotation in the magnetic Weyl semimetal Co2MnGa at room temperature

Abstract

We report measurement of terahertz anomalous Hall conductivity and Faraday rotation in the magnetic Weyl semimetal ${\mathrm{Co}}_{2}\mathrm{MnGa}$ 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 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ 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-principles calculation also supports the frequency-independent intrinsic anomalous Hall conductivity at low frequency. We also find a thickness-independent Faraday rotation of 59 $(\ifmmode\pm\else\textpm\fi{}6)$ 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 ${\mathrm{m}}^{\ensuremath{-}1} {\mathrm{T}}^{\ensuremath{-}1}$ at room temperature and the large Hall angle around $8.5%$ from 0.2--1.5 THz indicate that ${\mathrm{Co}}_{2}\mathrm{MnGa}$ is promising for THz spintronics at room temperature.