Fulde-Ferrell-Larkin-Ovchinnikov state in a perpendicular field of quasi two-dimensional CeCoIn5

TL;DR

This study provides evidence for the FFLO state in CeCoIn5 under a perpendicular magnetic field, revealing differences in phase diagram topology and quasiparticle spectra compared to parallel field configurations.

Contribution

First NMR evidence of FFLO state in CeCoIn5 with a perpendicular magnetic field, highlighting key differences from parallel field cases.

Findings

FFLO state confirmed in perpendicular field configuration.

Significant reduction of FFLO region compared to parallel field.

Altered quasiparticle excitation spectrum in the FFLO phase.

Abstract

A Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state was previously reported in the quasi-2D heavy fermion CeCoIn5 when a magnetic field was applied parallel to the ab-plane. Here, we conduct 115^In NMR studies of this material in a PERPENDICULAR field, and provide strong evidence for FFLO in this case as well. Although the topology of the phase transition lines in the H-T phase diagram is identical for both configurations, there are several remarkable differences between them. Compared to H//ab, the FFLO region for H perpendicular to the ab-plane shows a sizable decrease, and the critical field separating the FFLO and non-FFLO superconducting states almost ceases to have a temperature dependence. Moreover, directing H perpendicular to the ab-plane results in a notable change in the quasiparticle excitation spectrum within the planar node associated with the FFLO transition.