Phase diagram of unconventional superconductors on triangular lattices

The superconducting system in the two dimensional triangular lattice is investigated by the mean-field treatment of a simple effective model. We calculate the phase diagram of this kind of superconductor for various pairing symmetries and interactions as well as electron occupancies. It is found that the p(x)+ip(y)-, d+id'-, and f- wave superconducting states are stabilized in different doping regions, and there exist superconducting phase transitions by varying the carrier concentration in the system. The relevance of our results to the recently discovered superconductor, Na-x CoO2 - yH(2)O, is briefly discussed.