c-Axis conductivity and intrinsic Josephson effects in YBa2Cu3O7-delta

We have observed intrinsic Josephson coupling between CuO2 double layers of YBa2CU3O7-delta by direct detection of ac and de Josephson effects. The crucial points were a reduction of the junction size to the 1-2 mu m range and a weakening of the interlayer coupling via oxygen depletion of the CuO chains. As a result we obtained distinct signatures in the I-V characteristics and 11 GHz microwave emission caused by ac Josephson currents. The temperature dependence of the critical current supports the idea of a superconductor-insulator-superconductor interlayer tunneling mechanism.