Superconductivity in Uranium Compounds

TL;DR

This paper presents a microscopic theory explaining how magnetization fluctuations in ferromagnetic uranium compounds induce equal spin pairing superconductivity, and discusses experimental phenomena like the upper critical field behavior in UCoGe.

Contribution

It introduces a theoretical framework linking magnetization fluctuations to superconductivity in uranium compounds with orthorhombic symmetry, explaining experimental observations.

Findings

Magnetization fluctuations induce equal spin pairing superconductivity.

The increase in upper critical field is due to enhanced pairing interaction.

Predicted similar phenomena at higher magnetic fields along different axes.

Abstract

On the basis of microscopic theory it is demonstrated how the coupling between the electrons by means of magnetization fluctuations in ferromagnetic metal with orthorhombic symmetry gives rise equal spin pairing superconducting state with general form of the order parameter dictated by symmetry. The strong upturn of the upper critical field along $b$-direction above 5 Tesla in UCoGe is explained by the increase of pairing interaction caused by the suppression of the Curie temperature by magnetic field parallel to b-axis. It is proposed that similar phenomenon at much higher field must take place also for the field directed along the magnetically hardest a-direction.