Possible pairing symmetry in the two-dimensional t-J model on square and triangular lattices

To investigate effects of geometrical frustration on the possibility of superconductivity and its pairing symmetry in the strongly correlated electron system, we calculate the high-temperature series for the equal-time pairing correlation in the two-dimensional t-J model on square and triangular lattices. In the square lattice where the d-wave superconductivity is expected in the ground state, it is found that d-wave pairing correlation really grows with lowering the temperature. In the triangular lattice with t>0, d-wave pairing correlation also shows an enhancement. Since resonating valence bond (RVB)-like behavior is observed in this case, we speculate that the RVB superconductivity is realized. In contrast, in the case of t<0 on the triangular lattice, various pairing symmetries compete with each other. Particularly in the low-density region where the Fermi surface is disconnected, we find the possibility of f-wave superconductivity, which seems to be related to the ferromagnetic tendency in small J region.