Double-stage continuous-discontinuous superconducting phase transition in the Pauli paramagnetic limit of a 3D superconductor: the URu$%_{2}$Si$_{2}$ case

TL;DR

This paper confirms a theoretical prediction of a double-stage superconducting phase transition in URu$_{2}$Si$_{2}$, involving a transition to a nonuniform FFLO state followed by a transition to a uniform SC state, supported by experimental observations.

Contribution

It provides experimental evidence for a double-stage SC phase transition in a 3D paramagnetic superconductor, aligning with non-perturbative theoretical predictions.

Findings

Suppression of de-Haas van-Alphen oscillations confirms the phase transition.

Evidence supports a transition to a nonuniform FFLO state.

Transition sequence matches theoretical predictions and thermal conductivity data.

Abstract

The sharp suppression of the de-Haas van-Alphen oscillations observed in the mixed superconducting (SC) state of the heavy fermion compound URu$_{2}$Si$% _{2}$ is shown to confirm a theoretical prediction of a narrow double-stage SC phase transition, smeared by fluctuations, in a 3D paramagnetically-limitted superconductor. The predicted scenario of a second order transition to a nonuniform (FFLO) state followed by a first order transition to a uniform SC state, obtained by using a non-perturbative approach, is also found to be consistent with recent thermal conductivity measurements performed on this material.