Effect of Delocalized Vortex Core States on the Specific Heat of Nb

TL;DR

This study investigates how delocalized vortex core states influence the electronic specific heat in niobium, revealing a sublinear magnetic field dependence linked to quasiparticle delocalization.

Contribution

It provides experimental evidence of delocalized vortex core states affecting specific heat, highlighting complexities in interpreting measurements on type-II superconductors.

Findings

Electronic specific heat coefficient gamma(T,B) is sublinear in B above H_{c1}

Delocalization of quasiparticles bound to vortex cores affects thermodynamic properties

Emphasizes importance of field-cooled conditions in specific heat measurements

Abstract

The magnetic field (B) dependence of the electronic specific heat for a simple BCS type-II superconductor has been determined from measurements on pure niobium (Nb). Contrary to expectations, the electronic specific heat coefficient gamma(T,B) is observed to be a sublinear function of B at fields above the lower critical field H_{c1}. This behavior is attributed to the delocalization of quasiparticles bound to the vortex cores. The results underscore the ambiguity of interpretation that arises in specific heat studies of this kind on newly discovered type-II superconductors, and also emphasize the need to such measurements under field-cooled conditions.