Field Evolution of Coexisting Superconducting and Magnetic Orders in CeCoIn$_5$

TL;DR

This study uses NMR to investigate the coexistence and evolution of superconducting and magnetic orders in CeCoIn$_5$, revealing a field-induced magnetic order coexisting with a modulated superconducting phase and proposing a revised phase diagram.

Contribution

It provides microscopic insights into the magnetic order and its coexistence with superconductivity in CeCoIn$_5$, including the orientation of magnetic moments and the phase diagram revision.

Findings

Identification of magnetic order stabilized above 10.2 T in the superconducting state

Evidence of coexistence of magnetic order with a modulated superconducting phase

Proposal of a revised phase diagram with a region dominated by spin fluctuations

Abstract

We present nuclear magnetic resonance (NMR) measurements on the three distinct In sites of CeCoIn$_5$ with magnetic field applied in the [100] direction. We identify the microscopic nature of the long range magnetic order (LRO) stabilized at low temperatures in fields above 10.2 T while still in the superconducting (SC) state. We infer that the ordered moment is oriented along the $\hat c$-axis and map its field evolution. The study of the field dependence of the NMR shift for the different In sites indicates that the LRO likely coexists with a modulated SC phase, possibly that predicted by Fulde, Ferrell, Larkin, and Ovchinnikov. Furthermore, we discern a field region dominated by strong spin fluctuations where static LRO is absent and propose a revised phase diagram.