EXTENDED BOUND-STATES AND RESONANCES OF 2 FERMIONS ON A PERIODIC LATTICE

The high-T-c cuprates are possible candidates for d-wave superconducti vity, with the Cooper pair wave function belonging to a nontrivial irr educible representation of the lattice point group. We argue that this d-wave symmetry is related to a special form of the fermionic kinetic energy and does not require any novel pairing mechanism. In this cont ext, we present a detailed study of the bound states and resonances fo rmed by two lattice fermions interacting via a nonretarded potential t hat is attractive for nearest neighbors but repulsive for other relati ve positions. In the case of strong binding, a pair formed by fermions on adjacent lattice sites can have a small effective mass, thereby im plying a high condensation temperature. For a weakly bound state, a pa ir with nontrivial symmetry tends to be smaller in size than an s-wave pair. These and other findings are discussed in connection with the p roperties of high-T-c cuprate superconductors.