Fermi surface and topology of multiband superconductor BeAu

TL;DR

This paper investigates the topological electronic structure of the multiband superconductor BeAu, revealing complex Fermi surface topology, Weyl points, and potential topological superconducting phases with high Chern numbers.

Contribution

It provides the first comprehensive first-principles analysis of BeAu's electronic structure, identifying topological features and their implications for superconductivity.

Findings

Identification of multiple Weyl points near the Fermi level.

Discovery of a Fermi surface with a Chern number of +6.

Evidence of multigap superconductivity linked to orbital inhomogeneity.

Abstract

The chiral material BeAu was recently identified as a multiband type-I superconductor with a critical temperature of 3.2 K. As a member of the B20 crystal family (space group $P2_13$), its band structure hosts multifold fermions at high-symmetry points, unpaired Weyl points and even nodal surfaces. This renders BeAu an appealing system to investigate the interplay between superconductivity and topology. Here we present a comprehensive first-principles analysis of BeAu's electronic structure focusing on its Fermi surface's topology and the implications for superconductivity. Together with the presence of four- and six-fold fermions at high-symmetry points, we identify several additional isolated Weyl points near the Fermi level. We also determine the associated topological edge states -- the surface Fermi arcs. Computing the Chern number associated to different Fermi surface sheets, we show that BeAu harbors a $\nu = 4$ topological superconducting phase in the presence of $s$-wave pairing of alternating sign ($s_\pm$ pairing). Notably, we also identify a Fermi surface with a Chern number of +6; the highest value reported to date. Finally, our analysis reveals strong inhomogeneity in the orbital character of electronic states at the Fermi level, suggesting a link to the observed multigap superconductivity.