ROLES OF LO-PHONON AND SO-PHONON INDUCED POTENTIALS FOR A BIPOLARON IN THE SUPERCONDUCTOR

The bipolaronic system of an infinite quantum well, in which two elect rons or holes are weakly or intermediately coupled with both longitudi nal-optical (LO) and surface-optical (SO) phonons, may be applied on t he layer-type high-T-c superconductivity. Using the Lee-Low-Pines meth od, we have solved the Hamiltonian for the above bipolaron system. The numerical results show that, when the thickness of polar slab increas es, the binding energy increases for LO phonon contribution but decrea ses for SO phonon contribution. Taking the Coulombic repulsion into ac count, the effective interaction potential energy between the two hole s that form the stable bipolaron in a relatively thin polar slab of YB CO has a distinct equilibrium position at its minimum.