Anomalous Field-Temperature Phase Diagram of Superconductivity in Sn-Pb Solder

TL;DR

This study reveals an unusual superconducting phase diagram in Sn-Pb solder, showing anomalous behaviors in Sn regions under magnetic fields, likely due to flux trapping and vortex formation, differing from conventional superconductors.

Contribution

It reports the first observation of an anomalous Hc-T phase diagram in Sn-Pb solder, highlighting field-dependent superconductivity in Sn regions linked to flux trapping and vortex phenomena.

Findings

Hc(T) for Pb regions follows conventional behavior with Hc(0) ~ 800 Oe.

Hc(T) for Sn regions shows anomalous, field-dependent behavior.

Superconductivity in Sn regions is related to flux trapping and vortex formation.

Abstract

Sn-Pb solders are superconducting materials whose Sn and Pb are perfectly phase-separated. Recently, anomalous magnetic-flux trapping in a Sn45-Pb55 solder has been revealed where the magnetic fluxes are selectively trapped in the Sn regions due to the supercurrents in the surrounding Pb regions. Here, we report on the observation of the anomalous critical field (Hc)-temperature (T) phase diagram of superconductivity in the Sn45-Pb55 solder. Although the Hc(T) for the Pb regions decreases with increasing field as in normal type-I superconductors and is consistent with the conventional trend with Hc(0) ~ 800 Oe, the Hc(T) for the Sn regions exhibits anomalous behaviors. The most noticeable trend was observed in the field-cooled (under 1500 Oe) solder. The Hc-T phase diagram for the Sn regions largely varies when the applied external field is reversed, and Tc increases with increasing field amplitude when H < 0 Oe is applied. On the basis of the flux trapping and the observed anomalous Hc-T phase diagrams, we propose that the field-robust superconductivity in the Sn regions is related to the ferromagnetically-aligned magnetic fluxes (or formation of vortices) in the Sn regions of the Sn45-Pb55 solder.