c-axis resistivity in high-T-c superconductors

The interactions between polarons and the anharmonic vibrations of the apical oxygen atoms in the normal state of YBa2Cu3O7-delta superconductors have been studied by using a path integral formalism. The temperature effects in the distribution of double-well potentials associated with the anharmonic modes have been taken into account. It is shown that the c-axis electrical resistivity depends linearly on temperature for intermediate values of the overall electron-phonon coupling, whereas strong anharmonicity induces a nonmetallic behavior as a consequence of trapping of the charge carriers.