Intrinsic Berry curvature driven anomalous Nernst thermopower in the semimetallic Heusler alloy CoFeVSb

Abstract

Understanding of spin-heat coupling mechanisms and magnetothermoelectric phenomena, including the anomalous Nernst effect (ANE), in emergent quaternary Heusler alloys is of practical importance for applications in thermal management and energy harvesting. Here, we demonstrate an intrinsic Berry curvature mediated anomalous Nernst thermopower in CoFeVSb, which orders magnetically at high temperature (${T}_{C}\ensuremath{\approx}850\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) with a large saturation magnetization of $\ensuremath{\approx}2.2\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{f}.\mathrm{u}.$ at room temperature. We show that the electron-electron elastic and electron-magnon inelastic scattering dominate longitudinal electrical transport at low temperatures ($T\ensuremath{\le}50\phantom{\rule{0.28em}{0ex}}\mathrm{K}$), whereas the electron-phonon and electron-magnon scatterings govern it at higher $\phantom{\rule{0.28em}{0ex}}T$. The longitudinal thermopower is resulted mainly from the diffusive contribution with a very large longitudinal Seebeck coefficient ($42\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 395 K). The value of the anomalous Nernst coefficient (${S}_{\mathrm{ANE}}$) for CoFeVSb at room temperature is $0.039\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ which is higher than the compressively strained $\mathrm{SrRu}{\mathrm{O}}_{3}$ film ($0.03\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$) as well as the spin gapless semiconductor CoFeCrGa ($0.018\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$). On lowering $T$, both the ordinary Nernst coefficient and carrier mobility increase but an opposite trend is found for ${S}_{\mathrm{ANE}}$. Our ab initio simulations reveal the topological semimetallic nature of CoFeVSb with a pair of Weyl points. These Weyl crossings result in a significant contribution to the Berry curvature, leading to an intrinsic anomalous Hall conductivity (${\ensuremath{\sigma}}_{xy}^{\mathrm{AHE}}$) of $\ensuremath{\approx}85$ S/cm, which matches well with experiment (77 S/cm at 2 K). Our experimental findings and ab initio calculations support the dominance of the intrinsic Berry curvature in the observed ANE. The ratio of ${\ensuremath{\sigma}}_{xy}^{\mathrm{AHE}}$ to the transverse anomalous thermoelectric conductivity (${\ensuremath{\alpha}}_{xy}^{\mathrm{ANE}}$) shows an increasing trend with $T$ attaining a sizable fraction of $\phantom{\rule{0.28em}{0ex}}\frac{{k}_{B}}{e}\phantom{\rule{0.28em}{0ex}}(\ensuremath{\approx}0.35\frac{{k}_{B}}{e})$ at room temperature.