Coexistence of spin density wave, d-wave singlet and staggered π-triplet superconductivity

We have studied the competition and coexistence of staggered triplet superconductivity (SC) with d-wave singlet SC and spin density waves (SDWs) in the mean-field approximation. Detailed numerical studies demonstrate that particle-hole asymmetry mixes these states and therefore they are simultaneously present. Even more interesting were the results of our study of the influence of a uniform magnetic field. We observe novel transitions that show the characteristics of Fulde-Ferrel phases, yet they concern transitions to different combinations of the above orders. For example, above a given field, in a particle-hole symmetric system we observe a transition from d-wave singlet SC to a state in which d-wave singlet SC coexists with staggered triplet SC and SDWs. We believe our results may provide, among others, a direct explanation of recent puzzles about the Fulde-Ferrel like states that are apparently observed in CeCoIn(5).