Half-Quantum Vortices in Nematic and Chiral Phases of $^3$He

TL;DR

This paper theoretically investigates the stability and structure of half-quantum vortices in superfluid $^3$He confined in anisotropic Nafen aerogel, revealing new topological and magnetic signatures in nematic and chiral phases.

Contribution

It predicts a second chiral phase in $^3$He-Nafen and analyzes the properties of HQVs, including their signatures in these novel phases.

Findings

Identification of a chiral superfluid phase with broken time-reversal symmetry.

Prediction of magnetic and topological signatures of HQVs.

Analysis of HQV structures in both nematic and chiral phases.

Abstract

We report theoretical results for the stability of half-quantum vortices (HQVs) in the superfluid phases of $^3$He confined in highly anisotropic Nafen aerogel. Superfluidity of $^3$He confined in Nafen is the realization of a "nematic superfluid" with Cooper pairs condensed into a single p-wave orbital aligned along the anisotropy axis of the Nafen aerogel. In addition to the nematic phase, we predict a second "chiral" phase that onsets at a lower transition temperature. This chiral phase spontaneously breaks time-reversal symmetry and is a topological superfluid. Both superfluid phases are equal-spin pairing condensates that host arrays of HQVs as equilibrium states of rotating superfluid $^3$He. We present results for the structure of HQVs, including magnetic and topological signatures of HQVs in both the nematic and chiral phases of $^3$He-Nafen.