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

TL;DR

This study visualizes spin-polarized Weyl cones in ferromagnetic Heusler films and links their topological properties to a giant anomalous Nernst effect, promising for room-temperature thermoelectric applications.

Contribution

It provides direct experimental visualization of spin-polarized Weyl cones in ferromagnetic Heusler films and demonstrates their impact on large anomalous Nernst effects.

Findings

Visualization of spin-polarized Weyl cones and surface states.

Observation of high anomalous Nernst thermopower (~6.2 μV/K) at room temperature.

Correlation between Weyl cone proximity to Fermi level and transport properties.

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 $ab\ initio$ 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 $\sim 6.2$ $\rm \mu V K^{-1}$ 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.