Phase transition between the Bragg Glass and a disordered Phase in Nb3Sn, detected by 3rd harmonics of the AC magnetic susceptibility

TL;DR

This study investigates the phase transition between the Bragg Glass and disordered phases in Nb3Sn superconductors, revealing the importance of higher harmonics in AC susceptibility measurements to detect this transition up to high magnetic fields.

Contribution

First observation of Peak Effect in Nb3Sn using 1st harmonics and detection of the phase transition up to 19 T through 3rd harmonics analysis.

Findings

Peak Effect observed between 3T and 13T with 1st harmonics

Phase transition detected up to 19 T using 3rd harmonics

Higher harmonics are essential for studying vortex matter transitions

Abstract

We report additional experimental evidences about the presence of an universal behavior in the Field-Temperature Phase Diagram of Type II Superconductors. This behavior is characterized by a phase transition in the vortex matter between the disordered and the Bragg Glass phase. The experimental detection of a Peak Effect phenomenon has been proved to be strictly connected to the existence of this phase transition. In this paper, we show the first observation of a Peak Effect in the compound Nb3Sn, by using 1st harmonics of the AC magnetic susceptibility. Peak Effect has been detected at fields between 3T and 13T, whereas it is not observable at higher fields. This seems to be in contrast with the theoretical predictions of such a phase transition at all fields. Nevertheless, by measuring the 3rd harmonics of the AC susceptibility, this phase transition has been detected up to our highest available field (19 T), thus demonstrating the necessity of the higher harmonics analysis in studying these topics and moreover proving the validity of the theoretical predictions.