Field-Induced Spin-Exciton Condensation in dx2-y2-wave Superconducting   CeCoIn5
  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 dx2 -y2 -wave superconductivity and induces 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 (that can be commensurate or incommensurate close to commensuration). The applications of the model are addressed to the low-temperature/high-magnetic-field phase of CeCoIn5 [M. Kenzelmann et al., Science 321, 1652 (2008), Phys. Rev. Lett. 104, 127001 (2010)]. 
V. P. Michal and V. P. Mineev
cond-mat.supr-con cond-mat.str-el