Stable fractional flux vortices in mesoscopic superconductors

TL;DR

This paper demonstrates that mesoscopic effects can stabilize fractional flux vortices in s-wave two-gap superconductors, allowing flux values to be arbitrary fractions of the flux quantum, which can be directly measured.

Contribution

It reveals that size effects in mesoscopic s-wave two-gap superconductors enable stable fractional vortices, a phenomenon previously associated mainly with unconventional superconductors.

Findings

Fractional flux vortices are stabilized by mesoscopic size effects.

Flux values can be arbitrary fractions of the flux quantum.

Fractional vortices can be directly measured from magnetic field distributions.

Abstract

Conventional superconductors have vortices carrying integer multiples of magnetic flux quantum while unconventional ones, with p- or d-wave order parameter, allow half-integer fluxes. Here we show that mesoscopic size effects stabilize fractional flux vortices in the thermodynamical ground state of s-wave two-gap superconductors. The value of these fluxes can be an arbitrary fraction of flux quantum and can be measured directly from distributions of magnetic fields on the samples.