Possible Fulde-Ferrell-Larkin-Ovchinnikov State in CeCoIn_5

TL;DR

This paper investigates the presence of an FFLO state in CeCoIn_5 through magnetothermal conductivity and upper critical field measurements, suggesting its existence along certain directions and predicting observable quasiparticle density features.

Contribution

It provides experimental evidence for the FFLO state in CeCoIn_5 along the a-axis and predicts its quasiparticle density of states structure, advancing understanding of unconventional superconductivity.

Findings

FFLO state observed along H parallel a at low temperatures

No FFLO state detected along H parallel c

Quasiparticle density of states in FFLO state shows complex peaks

Abstract

Angular dependent magnetothermal conductivity experiments on CeCoIn_5 indicate that this compound is a d-wave superconductor. In this study, the low-temperature behavior of the upper critical field is measured in a single crystal of CeCoIn_5 along the directions H parallel a and H parallel c. The data is compared with model calculations of the upper critical field in a d-wave superconductor. It is found that the observed H_c2(T) along H parallel a is consistent with a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state at low temperatures, T < 0.7K, whereas for H parallel c the FFLO state appears to be absent in CeCoIn_5. Furthermore, it is predicted that the quasiparticle density of states in the FFLO state exhibits a complex peak structure which should be observable by scanning tunneling microscopy.