Evolution of Paramagnetic Quasiparticle Excitations Emerged in the High-Field Superconducting Phase of CeCoIn5

TL;DR

This study uses NMR measurements to investigate a high-field phase of CeCoIn5, revealing the emergence of spatially distributed quasiparticles and evidence for FFLO state formation with coexisting spin-density wave order.

Contribution

It provides direct NMR evidence for the spatial distribution of quasiparticles and the formation of FFLO and spin-density wave states in CeCoIn5 under high magnetic fields.

Findings

Evidence for spatially distributed normal quasiparticle regions.

Confirmation of FFLO state with nodal plane formation.

Induction of uniform spin-density wave in the FFLO phase.

Abstract

We present In NMR measurements in a novel thermodynamic phase of CeCoIn5 in high magnetic field, where exotic superconductivity coexists with the incommensurate spin-density wave order. We show that the NMR spectra in this phase provide direct evidence for the emergence of the spatially distributed normal quasiparticle regions. The quantitative analysis for the field evolution of the paramagnetic magnetization and newly-emerged low-energy quasiparticle density of states is consistent with the nodal plane formation, which is characterized by an order parameter in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The NMR spectra also suggest that the spatially uniform spin-density wave is induced in the FFLO phase.