Formation of multi-quanta vortices in superconductors: electronic, calorimetric and magnetic evidence

TL;DR

This paper demonstrates that transitions between multi-quanta vortices and individual vortices in mesoscopic superconductors can be detected through heat capacity and magnetic susceptibility measurements, revealing changes in quasiparticle states.

Contribution

It provides experimental evidence linking vortex state transitions to measurable thermodynamic and magnetic properties in superconductors.

Findings

Heat capacity exhibits clear jumps during vortex transitions.

Magnetic susceptibility shows sharp changes at vortex state boundaries.

Transitions can be controlled by external parameters like magnetic field and temperature.

Abstract

The ground state with vorticity larger than one in mesoscopic superconductors in applied magnetic field may manifest as a `giant'-vortex, where all vortices coalesce into a single singularity of the order parameter. Such a multi-quanta vortex may split into individual vortices (and vice versa) as a function of e.g. applied current, magnetic field or temperature. Here we show that such transitions can be identified by heat-capacity measurements, as the formation or splitting of a giant-vortex results in a clear jump in measured heat capacity vs. external drive. We attribute this phenomenon to an abrupt change in the density of states of the quasiparticle excitations in the vortex core(s), and further link it to a sharp change of the magnetic susceptibility at the transition - proving that formation of a giant-vortex can also be detected by conventional magnetometry.