Antiferromagnetism and Superconductivity in a Model with Extended Pairing Interactions

The competition between antiferromagnetism and the d+ id superconducting state is studied in a model with near and next near neighbour interactions in the absence of any on-site repulsion. A mean field study shows that it is possible to have simultaneous occurrence of an antiferromagnetic and a singlet d + id superconducting state in this model. In addition, such a coexistence generates a triplet d+ id superconducting order parameter with centre of mass momentum Q = (π, π) dynamically having the same orbital symmetry as the singlet superconductor. Inclusion of next nearest neighbour hopping in the band stabilises the dxy superconducting state away from half filling, the topology of the phase diagram, though, remains similar to the near neighbour model. In view of the very recent observation of a broad region of coexistence of antiferrmagnetic and unconventional superconducting states in organic superconductors, the possibility of observation of the triplet state has been outlined. PACS Nos. 74.20.-z, 74.72.-h