Intertwined Orders in Heavy-Fermion Superconductor CeCoIn5

Duk Y Kim,Roman Movshovich,Michel Kenzelmann,J D Thompson,Franziska Weickert,Eric D Bauer,Shi-Zeng Lin,Filip Ronning

doi:10.1103/physrevx.6.041059

Duk Y Kim, Roman Movshovich + Show 6 more

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https://doi.org/10.1103/physrevx.6.041059

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Abstract

The appearance of spin-density-wave (SDW) magnetic order in the low-temperature and high-field corner of the superconducting phase diagram of CeCoIn$_5$ is unique among unconventional superconductors. The nature of this magnetic $Q$ phase is a matter of current debate. Here, we present the thermal conductivity of CeCoIn$_5$ in a rotating magnetic field, which reveals the presence of an additional order inside the $Q$ phase that is intimately intertwined with the superconducting $d$-wave and SDW orders. A discontinuous change of the thermal conductivity within the $Q$ phase, when the magnetic field is rotated about antinodes of the superconducting $d$-wave order parameter, demands that the additional order must change abruptly together with the recently observed switching of the SDW. A combination of interactions, where spin-orbit coupling orients the SDW, which then selects the secondary $p$-wave pair-density-wave component (with an average amplitude of 20\% of the primary $d$-wave order parameter), accounts for the observed behavior.

Highlights

Magnetism is considered to be detrimental to conventional superconductivity, which is mediated by lattice vibrations— phonons [1]
We present the thermal conductivity of CeCoIn5 in a rotating magnetic field, which reveals the presence of an additional order inside the Q phase that is intimately intertwined with the superconducting d-wave and SDW orders
Measurements on the thermal conductivity of CeCoIn5 in a rotating magnetic field reveal the nature of the Q phase

Summary

INTRODUCTION

Magnetism is considered to be detrimental to conventional superconductivity, which is mediated by lattice vibrations— phonons [1]. CeCoIn5 presents a unique case among all unconventional superconductors wherein a novel magnetic state, the so-called Q phase, develops at high fields and requires superconductivity for its very existence This Q phase was originally suggested [6,7,8] to be a realization of spatially inhomogeneous superconductivity, the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state [9,10]. One recently proposed scenario explains the hypersensitivity as being due to the magnetic field lifting the degeneracy of the direction of QSDW via spin-orbit coupling [28], without requiring any additional order besides the existing superconducting d-wave and SDW orders. Another scenario introduces the spatially inhomogeneous Fulde-Ferrell-Larkin-. Measurements on the thermal conductivity of CeCoIn5 in a rotating magnetic field reveal the nature of the Q phase

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