Abstract
We have investigated the coupling between layers in high- superconductors by direct measurements of all dc and ac Josephson effects with current flow in the c-axis direction. The measurements have been performed on small single crystals of , (, , and and on a-axis-oriented thin films. The results clearly show that all materials behave like stacks of superconductor-insulator-superconductor Josephson junctions. The current-voltage characteristics exhibit large hystereses and multiple branches, which can be explained by a series connection of highly capacitive junctions. From the modulation of the critical current in a magnetic field parallel to the layers, we infer a junction thickness of approximately 15 Å. In our microwave emission experiments we were able to prove explicitly that every pair of double or triple layers forms a working Josephson contact. An exception is , where only flux-flow behavior has been observed.
- Received 19 July 1993
DOI:https://doi.org/10.1103/PhysRevB.49.1327
©1994 American Physical Society