Impurity-induced antiferromagnetic order in Pauli-limited nodal superconductors: application to heavy fermion CeCoIn5

TL;DR

This paper models the coexistence of antiferromagnetism and d-wave superconductivity in CeCoIn5, revealing that magnetic impurities can induce a Q-phase at low fields, aligning with experimental observations.

Contribution

It demonstrates that dilute magnetic impurities can nucleate a long-range ordered Q-phase in CeCoIn5 even without an external magnetic field, providing a new understanding of impurity effects.

Findings

Magnetic impurities induce the Q-phase at lower magnetic fields.

Impurities cooperate via RKKY interactions to produce long-range order.

The model aligns with recent neutron scattering experiments.

Abstract

We investigate the properties of the coexistence phase of itinerant antiferromagnetism and nodal $d$-wave superconductivity (Q-phase) discovered in heavy fermion CeCoIn5 under applied magnetic field. We solve the minimal model that includes $d$-wave superconductivity and underlying magnetic correlations in real space to elucidate the structure of the $Q$-phase in the presence of an externally applied magnetic field. We further focus on the role of magnetic impurities, and show that they nucleate the Q-phase at lower magnetic fields. Our most crucial finding is that, even at zero applied field, dilute magnetic impurities cooperate via RKKY-like exchange interactions to generate a long-range ordered coexistence state identical to the Q-phase. This result is in agreement with recent neutron scattering measurements [S. Raymond et al., J. Phys. Soc. Jpn. {\bf 83}, 013707 (2014)].