Two-Phase Regime in the Magnetic Field-Temperature Phase Diagram of a Type-II Superconductor

TL;DR

This study investigates the magnetic field-temperature phase diagram of V3Si superconductors, revealing a two-phase regime and a possible first-order phase transition with a critical point.

Contribution

It provides experimental evidence for a two-phase regime and a first-order transition in a type-II superconductor's phase diagram.

Findings

Reversible magnetic moment-magnetic field isotherms resemble liquid-gas isotherms.

Hysteresis observed in magnetic moments below transition temperature.

Entropy change consistent with vortex density differences.

Abstract

The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of ${\rm V_{3}Si}$ have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However the magnetic moment-magnetic field isotherms are reversible and exhibit features that formally resemble the pressure-volume isotherms of the liquid-gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The entropy change, determined from the data using the Clausius-Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases.