Spin-polarized Weyl cones and gigantic anomalous Nernst effect in ferromagnetic Heusler films

Abstract

Weyl semimetals are characterized by the presence of massless band dispersion in momentum space. When a Weyl semimetal meets magnetism, large anomalous transport properties emerge as a consequence of its topological nature. Here, using $in-situ$ spin- and angle-resolved photoelectron spectroscopy combined with $abinitio$ calculations, we visualize the spin-polarized Weyl cone and flat-band surface states of ferromagnetic Co${}_2$MnGa films with full remanent magnetization. We demonstrate that the anomalous Hall and Nernst conductivities systematically grow when the magnetization-induced massive Weyl cone at a Lifshitz quantum critical point approaches the Fermi energy, until a high anomalous Nernst thermopower of $\sim 6.2$ $\mu \mathrm{V}{\mathrm{K}}^{-1}$ is realized at room temperature. Given this topological quantum state and full remanent magnetization, Co${}_2$MnGa films are promising for realizing high efficiency heat flux and magnetic field sensing devices operable at room temperature and zero-field.

25 pages, 5 figures, 1 table