Superconductivity induced by longitudinal ferromagnetic fluctuations in UCoGe

TL;DR

This study demonstrates that longitudinal ferromagnetic spin fluctuations in UCoGe are crucial for its superconductivity, with magnetic fields along the c axis suppressing these fluctuations and thereby affecting the superconducting state.

Contribution

The paper provides the first clear evidence linking ferromagnetic fluctuations directly to superconductivity in UCoGe through detailed experimental and theoretical analysis.

Findings

Superconductivity in UCoGe is closely coupled with longitudinal FM spin fluctuations.

Magnetic fields along the c axis suppress FM fluctuations and influence superconductivity.

Longitudinal FM spin fluctuations induce spin-triplet superconductivity in UCoGe.

Abstract

From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic (FM) superconductor UCoGe (T_Curie ~ 2.5 K and T_SC ~ 0.6 K), we show that superconductivity in UCoGe is tightly coupled with longitudinal FM spin fluctuations along the c axis. We found that magnetic fields along the c axis (H || c) strongly suppress the FM fluctuations and that the superconductivity is observed in the limited magnetic field region where the longitudinal FM spin fluctuations are active. These results combined with model calculations strongly suggest that the longitudinal FM spin fluctuations tuned by H || c induce the unique spin-triplet superconductivity in UCoGe. This is the first clear example that FM fluctuations are intimately related with superconductivity.