Structured Weyl Points in Spin-Orbit Coupled Fermionic Superfluids

TL;DR

This paper introduces a new topological structure called structured Weyl points, consisting of pairs of gapless spheres with distinct invariants, realized in spin-orbit coupled Fermi superfluids with Zeeman fields.

Contribution

It reveals the formation of structured Weyl points with complex topology in superfluid quasiparticle spectra, expanding understanding of topological phases in quantum gases.

Findings

Structured Weyl points consist of two non-degenerate gapless spheres.

Three topological invariants characterize these structures.

Realization in spin-orbit coupled Fermi gases with Zeeman fields.

Abstract

We demonstrate that a Weyl point, widely examined in 3D Weyl semimetals and superfluids, can develop a pair of non-degenerate gapless spheres. Such a bouquet of two spheres is characterized by three distinct topological invariants of manifolds with full energy gaps, i.e., the Chern number of a 0D point inside one developed sphere, the winding number of a 1D loop around the original Weyl point, and the Chern number of a 2D surface enclosing the whole bouquet. We show that such structured Weyl points can be realized in the superfluid quasiparticle spectrum of a 3D degenerate Fermi gas subject to spin-orbit couplings and Zeeman fields, which supports Fulde-Ferrell superfluids as the ground state.