Coexistence of ferromagnetism and superconductivity

TL;DR

This paper develops a comprehensive field-theoretic framework to describe the coexistence of p-wave, spin-triplet superconductivity with itinerant ferromagnetism, explaining how magnetic fluctuations enhance superconductivity in ferromagnetic materials.

Contribution

It introduces a unified theoretical approach to analyze the coexistence of ferromagnetism and superconductivity, including derivation of gap equations and phase diagrams.

Findings

Magnetic fluctuations are stronger on the ferromagnetic side, boosting superconducting critical temperature.

The phase diagram aligns with experimental data from UGe₂ and ZrZn₂.

Superconductivity is enhanced by magnetic fluctuations near the phase boundary.

Abstract

A comprehensive theory is developed that describes the coexistence of p-wave, spin-triplet superconductivity and itinerant ferromagnetism. It is shown how to use field-theoretic techniques to derive both conventional strong-coupling theory, and analogous gap equations for superconductivity induced by magnetic fluctuations. It is then shown and discussed in detail that the magnetic fluctuations are generically stronger on the ferromagnetic side of the magnetic phase boundary, which substantially enhances the superconducting critical temperature in the ferromagnetic phase over that in the paramagnetic one. The resulting phase diagram is compared with the experimental observations in UGe_2 and ZrZn_2.