Field dependence of the vortex core size in a multi-band superconductor

TL;DR

This study investigates how the vortex core size in the multi-band superconductor NbSe2 varies with magnetic field, revealing different behaviors linked to its multiple energy gaps and proposing a model connecting core size reduction to thermal conductivity enhancement.

Contribution

It introduces a simple model that relates vortex core size reduction to delocalized core states and thermal conductivity, validated on NbSe2 and V3Si.

Findings

Rapid core size shrinkage at low fields due to small gap states

Field-independent core size above 4 kOe linked to large gap states

Model accurately describes vortex core behavior in multi-band and single-band superconductors

Abstract

The magnetic field dependence of the vortex core size in the multi-band superconductor NbSe2 has been determined from muon spin rotation measurements. The spatially extended nature of the quasiparticle core states associated with the smaller gap leads to a rapid field-induced shrinkage of the core size at low fields, while the more tightly bound nature of the states associated with the larger gap leads to a field-independent core size for fields greater than 4 kOe. A simple model is proposed for the density of delocalized core states that establishes a direct relationship between the field-induced reduction of the vortex core size and the corresponding enhancement of the electronic thermal conductivity. We show that this model accurately describes both NbSe2 and the single-band superconductor V3Si.