Thermoelectricity of the Ferromagnetic Superconductor UCoGe

TL;DR

This study investigates how magnetic field-induced changes in the Fermi surface of UCoGe influence its thermoelectric properties and superconductivity, revealing a topological transition near a critical magnetic field.

Contribution

It provides experimental evidence of a Fermi surface change in UCoGe under magnetic field, linking it to thermoelectric behavior and superconductivity enhancement.

Findings

Sharp thermopower peak at 11.1 T indicating Fermi surface modification

Sign change in thermopower at high fields suggesting topological transition

Correlation between Fermi surface change and superconductivity enhancement

Abstract

UCoGe exhibits superconductivity in the presence of ferromagnetism. When a field is applied along the b axis (perpendicular to the easy axis), ferromagnetism is weakened and superconductivity is enhanced. This enhancement has been attributed to an increase in coupling as observed in the enhanced effective mass produced by the critical fluctuations as the ferromagnetic transition is strongly suppressed. However it is also important to know if and how the Fermi surface changes near the critical point. Here we report measurements of the thermoelectricity of UCoGe which reveal a low carrier density metal. Under magnetic field applied along the b axis, a sharp peak is observed in the thermopower of UCoGe at H*=11.1T and low temperature which becomes broader at higher temperatures. At higher field, the thermopower changes sign which suggests a modification of the Fermi Surface. We analyze these results using a topological change in Fermi surface and show that this can explain both the thermopower and the enhanced superconductivity.