Vortex nucleation barriers and stable fractional vortices near boundaries in multicomponent superconductors

TL;DR

This paper investigates vortex nucleation barriers in multicomponent superconductors, revealing how fractional vortices near boundaries alter flux entry processes and challenge traditional models.

Contribution

It introduces a numerical method to calculate fluxoid penetration barriers considering intercomponent couplings, highlighting fractional vortex effects.

Findings

Fractional vortices can be stable near boundaries in multicomponent superconductors.

Multiple sphalerons and intermediate states exist due to complex energy landscapes.

The gauged string method enables precise calculation of nucleation barriers.

Abstract

The magnetization process of a superconductor is determined by the potential barrier for vortex nucleation and escape. In multicomponent superconductors, fractional vortices with a winding in the phase of only one of the components can be stable topological solitons that carry a fraction of the flux quantum. While the formation of such objects in the bulk costs logarithmically or linearly divergent energy, these objects were shown to be stable near samples' boundaries in the two-component London model. Therefore, the conventional Bean-Livingston picture of magnetic flux entry does not apply to these superconductors, since the entry process can involve fractionalization of a vortex. In this paper, we address the nonlinear problem of determining the potential barrier for fluxoid penetration in a multicomponent superconductor, including the effects of various intercomponent couplings, by using the recently developed gauged string method. The method allows numerically exact (i.e., convergent) calculation of a sphaleron configuration in a gauge theory and thus the height of the nucleation barrier. We show how the fractionalized nucleation processes result in multiple sphalerons and intermediate states due to the complex shape of the energy landscape of multicomponent superconductors.