Antiferromagnetic fluctuations and the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn5

TL;DR

This study investigates the stability and evolution of the FFLO superconducting state in CeCoIn5 under pressure, revealing its robustness and expansion despite suppression of antiferromagnetic spin fluctuations.

Contribution

It provides experimental evidence that the FFLO state in CeCoIn5 remains stable and expands under pressure, even as antiferromagnetic fluctuations are suppressed.

Findings

FFLO phase remains stable under pressure

FFLO phase expands as pressure increases

Antiferromagnetic fluctuations influence the FFLO state

Abstract

The heavy-fermion superconductor CeCoIn5 is the first material, where different experimental probes show strong evidence pointing to the realization of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The inhomogeneous superconducting FFLO state with a periodically modulated order parameter was predicted to appear in Pauli-limited, sufficiently clean type-II superconductors already more than 40 years ago. On the other hand, CeCoIn5 is supposed to be close to a magnetic quantum critical point (QCP) showing strong antiferromagnetic (AFM) spin fluctuations (SF) at atmospheric pressure. We studied the evolution of the FFLO phase away from the influence of the strong AFM-SF by heat capacity experiments under pressure (0 GPa <= P <= 1.5 GPa, 0 T <= mu_0 H <= 14 T, and 100 mK <= T <= 4 K). Our results prove the stability of the the FFLO phase under pressure. It even expands, while the Pauli-limiting becomes weaker and the AFM-SF are suppressed. This shows the intriguing influence of the AFM-SF on the FFLO state.