Visualizing half-metallic bulk band structure with multiple Weyl cones of the Heusler ferromagnet

TL;DR

This study uses angle-resolved photoelectron spectroscopy to reveal the bulk band structure of Co$_2$MnGe, confirming its half-metallicity and identifying Weyl cones that suggest topological properties influencing transport phenomena.

Contribution

It provides experimental evidence of the half-metallic nature and topological Weyl cones in Co$_2$MnGe, linking electronic structure to potential topological effects.

Findings

Confirmation of half-metallicity with no minority spin Fermi surface contribution

Identification of Weyl cones near the X point

Implications for large anomalous Hall and Nernst effects

Abstract

Using a well-focused soft X-ray synchrotron radiation beam, angle-resolved photoelectron spectroscopy was applied to a full-Heusler-type Co$_2$MnGe alloy to elucidate its bulk band structure. A large parabolic band at the Brillouin zone center and several bands that cross the Fermi level near the Brillouin zone boundary were identified in line with the results from first-principles calculations. These Fermi level crossings are ascribed to majority spin bands that are responsible for electron transport with extremely high spin polarization especially along the direction being perpendicular to the interface of magneto-resistive devices. The spectroscopy confirms there is no contribution of the minority spin bands to the Fermi surface, signifying half-metallicity for the alloy. Furthermore, two topological Weyl cones with band crossing points were identified around the $X$ point, yielding the conclusion that Co$_2$MnGe could exhibit topologically meaningful behavior such as large anomalous Hall and Nernst effects driven by the Berry flux in its half-metallic band structure.