Lattice instabilities and c-axis resistivity in high-Tc superconductors

We propose a general model to describe the coupling of polaronic charge carriers with double well potentials due to local lattice instabilities. A path integral formalism accounts for the retardation effects in the attractive polaron-polaron interaction mediated by the double well structure. The model is applied to the normal state of YBa2Cu3O7-δ superconductor and it is shown that the attractive forces are relevant in a strong coupling regime for realistic values of the input parameters. The calculated c-axis electrical resistivity shows a metallic like behaviour with deviations from a T linear dependence due to the role of the attractive interaction. The absolute values of resistivity are consistent with the experimental data in the case of strong electron-lattice coupling. © 1995