c-Axis Conductivity and Intrinsic Josephson Effects inYBa2Cu3O7−δ

Abstract

We have observed intrinsic Josephson coupling between ${\mathrm{CuO}}_2$ double layers of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ by direct detection of ac and dc Josephson effects. The crucial points were a reduction of the junction size to the $1–2\mu \mathrm{m}$ 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.