Giant Dampinglike-Torque Efficiency in Naturally Oxidized Polycrystalline <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mi>Ta</mml:mi><mml:mi>As</mml:mi></mml:mrow></mml:math> Thin Films

We report the measurement of efficient charge-to-spin conversion at room temperature in Weyl semimetal/ferromagnet heterostructures with both oxidized and pristine interfaces. Polycrystalline films semimetal, TaAs, are grown by molecular beam epitaxy on (001) GaAs interfaced a metallic ferromagnet (Ni$_{0.8}$Fe$_{0.2}$). Spin torque ferromagnetic resonance (ST-FMR) measurements samples an interface yield spin efficiency as large $\xi_{\mathrm{FMR}}=0.45\pm 0.25$ for 8 nm Ni$_{0.8}$Fe$_{0.2}$ layer thickness. By studying ST-FMR these varying thickness, we extract damping-like high $\xi_{\mathrm{DL}}=1.36\pm 0.66$. In (unoxidized) interface, has opposite sign to that observed ($\xi_{\mathrm{FMR}}=-0.27\pm 0.14$ 5 thickness). also find lower bound Hall conductivity ($424 \pm 110 \frac{\hbar}{e}$ S/cm) which is surprisingly consistent theoretical predictions single crystal semimetal state TaAs.