Skyrmion versus vortex flux lattices in p-wave superconductors

TL;DR

This paper demonstrates that skyrmion flux lattices in p-wave superconductors are energetically favored over vortex lattices, predicts their melting behavior, and proposes experimental methods for detection.

Contribution

It analytically compares skyrmion and vortex flux lattices, showing skyrmions are lower energy in p-wave superconductors and predicts their unique melting behavior.

Findings

Skyrmion lattices have lower free energy than vortex lattices in p-wave superconductors.

Skyrmion lattices do not melt near the lower critical field Hc1, unlike vortex lattices.

The paper proposes muSR experiments to detect skyrmion lattices.

Abstract

p-wave superconductors allow for topological defects known as skyrmions, in addition to the usual vortices that are possible in both s-wave and p-wave materials. In strongly type-II superconductors in a magnetic field, a skyrmion flux lattice yields a lower free energy than the Abrikosov flux lattice of vortices, and should thus be realized in p-wave superconductors. We analytically calculate the energy per skyrmion, which agrees very well with numerical results. From this, we obtain the magnetic induction B as a function of the external magnetic field H, and the elastic constants of the skyrmion lattice, near the lower critical field H_c1. Together with the Lindemann criterion, these results suffice to predict the melting curve of the skyrmion lattice. We find a striking difference in the melting curves of vortex lattices and skyrmion lattices: while the former is separated at all temperatures from the Meissner phase by a vortex liquid phase, the skyrmion lattice phase shares a direct boundary with the Meissner phase. That is, skyrmions lattices never melt near Hc1, while vortex lattices always melt sufficiently close to Hc1. This allows for a very simple test for the existence of a skyrmion lattice. Possible muSR experiments to detect skyrmion lattices are also discussed.