ELECTRONIC INHOMOGENEITIES, ELECTRON-LATTICE AND PAIRING INTERACTIONSIN HIGH-T-C SUPERCONDUCTORS

The presence of electronic inhomogeneities strongly reduces the screen ing of the electron-ion interaction in high-temperature superconductor s. This implies the existence of an non-totally screened long-range co ntribution to the electron-lattice coupling and opens an additional ch annel for the formation of copper pairs. We calculate the superconduct ing order parameter taking into account a) the long-range and the shor t-range parts of the electron-lattice interaction and b) the Coulomb r epulsion between charge-carriers. We show that whereas the long-range electron-lattice coupling determines the anisotropy of the order param eter, the Coulomb repulsion and the short-range interactions determine its symmetry. Thus, different high-T-c superconductors may have s- or d-wave symmetry, depending on the relative strength of the interactio ns involved in the pairing.