Theoretical Study on Coexistence of Ferromagnetism and Superconductivity

TL;DR

This paper theoretically investigates the coexistence of ferromagnetism and superconductivity using a two-dimensional Hubbard model, revealing conditions under which they can coexist and highlighting the role of electron bands.

Contribution

It provides a theoretical analysis of ferromagnetic and superconducting coexistence using third-order perturbation theory on a Hubbard model, emphasizing band interactions.

Findings

Superconductivity is generally more stable in the paramagnetic state.

Ferromagnetic superconductivity can occur via electron-electron correlations between specific bands.

Two-band interactions are crucial for coexistence of ferromagnetism and superconductivity.

Abstract

On the basis of a two-dimensional t-t' Hubbard model in ferromagnetic and paramagnetic states, the triplet superconducting mechanism is investigated by the third-order perturbation theory with respect to the on-site Coulomb interaction U. In general, the superconducting state is more stable in the paramagnetic state than in the ferromagnetic state. As a special case, the dominant ferromagnetic superconductivity is obtained by the electron-electron correlation between the electronlike majority and holelike minority bands. Furthermore, it is pointed out that in some cases the two bands play an essential role for the coexistence of superconductivity and ferromagnetism.