Anisotropic field response of specific heat for a ferromagnetic superconductor UCoGe in magnetic fields

TL;DR

This paper investigates the anisotropic response of specific heat and density of states in the ferromagnetic superconductor UCoGe under magnetic fields, revealing how magnetic field direction influences superconducting properties and anisotropy.

Contribution

The study provides detailed experimental analysis of anisotropic specific heat and magnetization in UCoGe, and compares these findings with related compounds to understand magnetic anisotropy effects.

Findings

Specific heat is abruptly suppressed when magnetic field is applied along the c axis.

Density of states response is anisotropic and slightly singular with respect to field angle.

Ising-type magnetic anisotropy persists even in the superconducting state.

Abstract

Magnetic-field-angle-resolved specific heat and magnetization measurements were conducted on a ferromagnetic superconductor UCoGe with remarkable anisotropic upper critical field $H_{\rm c2}$. Although $H_{\rm c2}$ reaches a high magnetic field ($\sim 20$~T) along the $b$ axis, it is small ($\sim~0.6$~T) when a magnetic field is applied along the magnetic easy $c$-axis. This study indicates that the specific heat is abruptly suppressed when the magnetic field is applied toward the $c$ axis from the $a$ and $b$ axes in the ferromagnetic state. The field response of density of states (DOS) is anisotropic, relative to the $c$ axis, and its angle dependence is slightly singular. The Ising-type magnetic anisotropy of the ferromagnetic state is dominant even in the anisotropic reinforced superconducting state. These facts indicate that the suppression of DOS may closely relate to the superconducting state. We theoretically analyze these findings together with URhGe and UTe$_2$ by highlighting the common and distinctive features among three compounds.