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

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. 83, 013707 (2014)JUPSAU0031-901510.7566/JPSJ.83.013707].