C-Axis Conductivity and Intrinsic Josephson Effects in YBa2Cu3O7- delta.

Abstract

We have observed intrinsic Josephson coupling between ${\mathrm{CuO}}_{2}$ double layers of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ by direct detection of ac and dc Josephson effects. The crucial points were a reduction of the junction size to the $1--2\ensuremath{\mu}\mathrm{m}$ range and a weakening of the interlayer coupling via oxygen depletion of the CuO chains. As a result we obtained distinct signatures in the $I\ensuremath{-}V$ 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.