Thermal fluctuations and vortex melting in the classical superconductor Nb3Sn from high-resolution specific-heat measurements

TL;DR

This study uses high-resolution specific-heat measurements to investigate thermal fluctuations and vortex melting in Nb3Sn, revealing critical fluctuation behavior and a transition from continuous to first-order vortex melting.

Contribution

The paper demonstrates the ability to detect small fluctuation anomalies in Nb3Sn and characterizes the vortex melting transition using novel calorimetry techniques.

Findings

Detection of a lambda anomaly near Hc2 line

Scaling laws consistent with critical fluctuations

Evidence of a vortex melting transition that can be driven first-order

Abstract

The range of critical thermal fluctuations in classical bulk superconductors is extremely small and especially in low fields hardly experimentally inaccessible. With a new type of calorimeter we have been able to resolve a small lambda anomaly within a narrow temperature range around the Hc2 line. We show that the evolution of the anomaly as a function of magnetic field follows scaling laws expected in the presence of critical fluctuations. The lower onset of the fluctuation regime shows many characteristics of a continuous solid-to-liquid transition in the vortex matter. It can be driven into a first-order vortex melting transition by a small AC field which helps the vortex matter to reach equilibrium.