Upper critical field in superconductors near ferromagnetic quantum critical points; UCoGe

TL;DR

This paper investigates the behavior of the upper critical magnetic field in the ferromagnetic superconductor UCoGe near quantum critical points, highlighting anisotropic and strong-coupling effects through model calculations.

Contribution

It provides a theoretical analysis of the anisotropic and strong-coupling behaviors of $H_{c2}$ in UCoGe, incorporating effects of non-analytic corrections in spin susceptibility.

Findings

Large anisotropy in $H_{c2}$ between a- and c-axes

Strong-coupling behavior in $H_{c2}^{ ext{parallel a}}$

Effects of non-analytic corrections on superconductivity

Abstract

We study the strong-coupling superconductivity near ferromagnetic quantum critical points, mainly focusing on the upper critical fields $H_{c2}$. Based on our simple model calculations, we discuss experimentally observed unusual behaviors of $H_{c2}$ in a recently discovered ferromagnetic superconductor UCoGe. Especially, the large anisotropy between $H_{c2}\parallel a$-axis and $H_{c2}\parallel c$-axis, and the strong-coupling behaviors in $H_{c2}^{\parallel a}$ are investigated. We also examine effects of non-analytic corrections in the spin susceptibility on the superconductivity, which can arise from effective long range interactions due to particle-hole excitations.