First-order phase transition by a spin-flip potential in BCS superconductivity

TL;DR

This paper investigates how introducing a spin-flip potential in a BCS superconductor can induce a first-order phase transition, revealing a complex phase diagram with a tricritical point similar to Ising models.

Contribution

It demonstrates that a spin-flip potential causes a first-order phase transition in BCS superconductivity, expanding understanding of impurity effects on superconducting phase transitions.

Findings

First-order phase transition induced by spin-flip potential.

Presence of a tricritical point in the phase diagram.

Topological similarity to Ising model phase diagrams.

Abstract

A spin-flip potential $V$ is introduced in a BCS Hamiltonian in order to study a possible thermodynamic effect that might be caused by the addition of a magnetic impurity in a superconductor. We found that the competition between the pairing and the spin-flip effect, caused by the interaction between the itinerant electrons and the spin of the impurity, gives rise to a first-order phase transition for certain values of $V$. The phase diagram shows a tricritical point in a frontier line which is topologically similar to those found in the phase diagrams of some Ising-like models.