Superconductivity in Uranium Ferromagnets

TL;DR

This paper reviews the physical properties and theoretical understanding of superconductivity in uranium ferromagnetic materials, highlighting triplet pairing mechanisms and explaining phenomena like reentrant superconductivity.

Contribution

It provides a microscopic theory linking magnetization fluctuations to triplet pairing and explains specific experimental observations in uranium ferromagnetic superconductors.

Findings

Coupling via magnetization fluctuations leads to triplet pairing.

Reentrant superconductivity explained in URhGe.

Superconducting states in uranium ferromagnets characterized by symmetry.

Abstract

The theoretical description and the survey of physical properties of superconducting states in the uranium ferromagnetic materials are presented. On the basis of microscopic theory is shown that the coupling between the electrons in these ferromagnetic metals by means of magnetization fluctuations gives rise the triplet pairing superconducting state and the general form of the order parameter dictated by the symmetry is established. The theory allows to explain some specific observations including peculiar phenomenon of reentrant superconductivity in URhGe in magnetic field perpendicular to the direction of spontaneous magnetization. In addition we describe several particular topics relating to uranium superconducting ferromagnets: (i) critical magnetic relaxation in dual localized-itinerant ferromagnets, (ii) phase transition to ferromagnetic state in Fermi liquid and UGe$_2$, (iii) superconducting ordering in ferromagnetic metals without inversion symmetry.