Coexistence of ferromagnetism and superconductivity: the role of kinetic interactions, kinetic correlations, and external pressure

TL;DR

This paper investigates how kinetic interactions, correlations, and external pressure influence the coexistence of ferromagnetism and superconductivity using a Hubbard model, revealing conditions under which they coexist or suppress each other.

Contribution

It introduces a Hubbard model with inter-site kinetic correlations to analyze the coexistence of ferromagnetism and superconductivity, highlighting the role of kinetic effects and external pressure.

Findings

Singlet superconductivity is suppressed by ferromagnetism.

Triplet superconductivity can be enhanced or depleted by ferromagnetism.

Ferromagnetism can coexist with singlet superconductivity via bandwidth changes.

Abstract

We use the Hubbard type model to describe the coexistence between superconductivity (SC) and ferromagnetism (F). Our Hamiltonian contains single-site and two-site interactions. All inter-site interactions will have included the inter-site kinetic correlation: $<c_{i\sigma}^{+}c_{j\sigma}>$, within the Hartree-Fock approximation. To obtain the SC transition temperature $T_{SC}$ and Curie temperature $T_{C}$ we use the Green's functions method. The numerical results show that the singlet SC is eliminated by F, but the triplet SC is either enhanced or depleted by F, depending on the carrier concentration and direction of a superconducting spin pair with respect to magnetization. The kinetic correlation is capable of creating superconductivity. We find that the ferromagnetism created by change of the bandwidth can coexist with singlet superconductivity. In the case of triplet superconductivity the ferromagnetism creates different critical SC temperatures for the $A_{1}$ and $A_{2}$ phase (the pair's spin parallel and antiparallel to magnetization, respectively).