Phenomenological study of spin-triplet ferromagnetic superconductors

TL;DR

This paper reviews the phenomenology of spin-triplet ferromagnetic superconductors using Ginzburg-Landau theory, focusing on phase stability, coexistence, and transition types influenced by magnetization and anisotropies.

Contribution

It provides a quasi-phenomenological analysis of the phase diagram and stability of coexistence phases in ferromagnetic superconductors, highlighting the effects of anisotropy and transition order.

Findings

The mixed phase of ferromagnetism and superconductivity is stable.

Phase transitions can be first or second order depending on the material.

Anisotropies influence phase diagram shape but not stability domains.

Abstract

Unconventional superconductivity with spin-triplet Cooper pairing is reviewed on the basis of the quasi-phenomenological Ginzburg-Landau theory. The superconductivity, in particular, the mixed phase of coexistence of ferromagnetism and unconventional superconductivity is triggered by the spontaneous magnetization. The mixed phase is stable whereas the other superconducting phases that usually exist in unconventional superconductors are either unstable, or, for particular values of the parameters of the theory, some of these phases are metastable at relatively low temperatures in a quite narrow domain of the phase diagram. The phase transitions from the normal phase to the phase of coexistence is of first order while the phase transition from the ferromagnetic phase to the coexistence phase can be either of first or second order depending on the concrete substance. The Cooper pair and crystal anisotropy are relevant to a more precise outline of the phase diagram shape and reduce the degeneration of the ground states of the system but they do not drastically influence the phase stability domains and the thermodynamic properties of the respective phases.