Vortex matter in $U(1)\times U(1)\times\mathbb{Z}_2$ phase-separated superconducting condensates

TL;DR

This paper investigates vortex solutions and magnetic responses in a two-component superconductor model with phase separation, revealing novel vortex structures combining features of vortices and domain walls, with implications for magnetic behavior.

Contribution

It introduces a new type of vortex that combines vorticity with domain wall properties, arising in a phase-separated two-component superconductor model with broken symmetry.

Findings

Existence of pipelike multiquanta vortices with localized magnetic flux.

Stable or metastable multiquanta vortices even in non-type-1 regimes.

Complex magnetic responses influenced by phase separation and vortex structures.

Abstract

We study the properties of vortex solutions and magnetic response of two-component $U(1)\times U(1)\times\mathbb{Z}_2$ superconductors, with phase separation driven by intercomponent density-density interaction. Such a theory can be viewed arising from the breakdown of $SU(2)$ symmetry by a biquadratic interaction between the components of the field. Depending on the symmetry-breaking term, there are two ground-state phases: one where both components of the doublet are equal (the miscible phase) and one where only one component assumes a non zero vacuum expectation value (the immiscible state). In the latter phase, the spectrum of topological excitations contains both domain walls and vortices. We show the existence of another kind of excitation that has properties of both topological excitations at the same time. They combine vorticity together with a circular domain wall, interpolating between inequivalent broken states, that shows up as a ring of localized magnetic flux. Asymptotically, this resembles a vortex carrying multiple flux quanta, but because the magnetic field is localized at a given distance from the center this looks like a pipe. The isolated multiquanta pipelike vortices can be either stable or metastable, even if the system is not type-1. We also discuss the response of such a system to an externally applied magnetic field.