Dimensionality driven enhancement of ferromagnetic superconductivity in URhGe

TL;DR

This study demonstrates that uniaxial stress can significantly enhance superconductivity in URhGe by tuning magnetic fluctuations, leading to higher critical temperatures and a merged superconducting phase under magnetic fields.

Contribution

It reveals how uniaxial stress modifies magnetic fluctuations and enhances superconductivity in URhGe, providing new insights into pairing mechanisms in ferromagnetic superconductors.

Findings

Superconducting Tc reaches 1K under stress, more than double the ambient value.

Uniaxial stress merges low and high field superconducting states.

Transverse magnetic fluctuations are crucial for pairing.

Abstract

In most unconventional superconductors, like the high-Tc cuprates, iron pnictides, or heavy fermion systems, superconductivity emerges in the proximity of an electronic instability. Identifying unambiguously the pairing mechanism remains nevertheless an enormous challenge. Among these systems, the orthorhombic uranium ferromagnetic superconductors have a unique position, notably because magnetic fields couple directly to ferromagnetic order, leading to the fascinating discovery of the re-emergence of superconductivity in URhGe at high field. Here we show that uniaxial stress is a remarkable tool allowing fine-tuning of the pairing strength. With a relatively small stress, the superconducting phase diagram is spectacularly modified, with a merging of the low and high field superconducting states and a significant enhancement of superconductivity. The superconducting critical temperature increases both at zero field and under field, reaching 1K, more than twice higher than at ambient pressure. The enhancement of superconductivity is directly related to a change of the magnetic dimensionality with an increase of the transverse magnetic susceptibility, demonstrating that in addition to the Ising-type longitudinal ferromagnetic fluctuations, transverse magnetic fluctuations also play an important role in the superconducting pairing.