C-AXIS TUNNELING BETWEEN ADJACENT SUPERCONDUCTING CUO2 BILAYERS OR TRILAYERS

We have investigated the subgap tunneling characteristics in single cr ystals of Bi2Sr2CaCu2O8+delta and thin films of Tl2Ba2Ca2Cu3O10+delta With intrinsic Josephson junctions in the resistive state. The low tem perature current voltage characteristics (IVC) exhibits a high subgap conductivity. The results are compared to a calculated IVC for tunnel junctions between two identical d-wave superconductors. The calculated quasiparticle branch agrees reasonable with the measured IVC. However , the presence of a small s-wave component can not be excluded. Beside s the global IVC we studied fine structures which were observed in the IVC of both materials. These structures can be explained by a resonan t coupling of infrared active c-axis phonons to the Josephson ac curre nts between adjacent pairs of superconducting layers.