NONPERTURBATIVE RESULTS FOR ATTRACTIVE HUBBARD PAIRINGS IN TRIANGULARLATTICES

The electron pairing problem is studied by means of the extended Hubba rd Hamiltonian. The original many-body problem is mapped onto a tight- binding one in a higher dimensional space, where the problem can be so lved in an exact way. In a triangular lattice, the effects of the frus tration of antibonding states on the electronic correlation are analyz ed in detail. It is found that the hole pairing is always stronger tha n the electron case, in contrast with the bipartite lattices, where th ere is a complete symmetry between electron and hole pairings. The gro und state of two holes, when the attractive nearest-neighbor interacti on is dominant, is surprisingly triplet and its wave function has dire ctional nodes. A pairing phase diagram for holes in triangular lattice s is also presented.