Texture in the Superconducting Order Parameter of CeCoIn_5 Revealed by Nuclear Magnetic Resonance

TL;DR

This study uses ^{115}In NMR to provide microscopic evidence of a spatially modulated superconducting order parameter in CeCoIn_5, supporting the existence of an FFLO state and revealing anomalous vortex core structures.

Contribution

It offers the first microscopic evidence for the FFLO state in CeCoIn_5 through NMR spectroscopy, linking spectral changes to spatial modulation of the superconducting order parameter.

Findings

NMR spectrum shows dramatic change below T*(H) near the critical field.

Results coincide with anomalies in specific heat and ultrasound velocity.

Indicates an anomalous electronic structure of vortex cores.

Abstract

We present a ^{115}In NMR study of the quasi two-dimensional heavy-fermion superconductor CeCoIn_5 believed to host a Fulde-Ferrel-Larkin-Ovchinnkov (FFLO) state. In the vicinity of the upper critical field and with a magnetic field applied parallel to the ab-plane, the NMR spectrum exhibits a dramatic change below T*(H) which well coincides with the position of reported anomalies in specific heat and ultrasound velocity. We argue that our results provide the first microscopic evidence for the occurrence of a spatially modulated superconducting order parameter expected in a FFLO state. The NMR spectrum also implies an anomalous electronic structure of vortex cores.