The implications of the spin exciton mechanism are exposed in the context of a spin density wave (SDW) instability occurring inside the superconducting phase of a layered heavy electron compound. In this model a magnetic field serves as a tuning parameter bringing the system to the point where the transverse spin correlations are enhanced due to $d_{x^2\text{−}{y}^2}$-wave superconductivity and inducing an instability to a phase with coexisting superconductivity and SDW order. The model considers electrons in a crystal with antiferromagnetic interactions and provides restrictions on the Fermi surface characteristics and on the ordering wave vector (which can be commensurate or incommensurate close to commensuration). The applications of the model are addressed to the low-temperature–high-magnetic-field phase of CeCoIn${}_5$ [M. Kenzelmann et al., Science 321, 1652 (2008); M. Kenzelmann et al., Phys. Rev. Lett. 104, 127001 (2010)].

• Received 21 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.052508