Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in CeCoIn5

TL;DR

This study provides experimental evidence for the existence of the FFLO inhomogeneous superconducting state in CeCoIn5, observed through specific heat measurements near the critical magnetic field, revealing a transition from second to first order and an internal anomaly.

Contribution

First experimental identification of the FFLO state in CeCoIn5 using specific heat measurements across different magnetic field orientations.

Findings

Superconducting transition becomes first order above 10 T for certain directions.

A second specific heat anomaly indicates FFLO state presence.

FFLO state occupies a smaller phase region for H || [001].

Abstract

We report specific heat measurements of the heavy fermion superconductor CeCoIn5 in the vicinity of the superconducting critical field H_{c2}, with magnetic field in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first order for field above 10 T for H || [110] and H || [100]. In the same range of magnetic field we observe a second specific heat anomaly within the superconducting state. We interpret this anomaly as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for H || [001], with FFLO state occupying a smaller part of the phase diagram.