Proximity-coupled high Tc Josephson junctions: Do they exist?

A significant portion of the worldwide effort to develop high-Tc Josephson junctions for electronic applications has been devoted to superconductor-normal-superconductor (SNS) junctions. This paper expands upon the authors recent review of this subject. Numerous groups have reported nominally-SNS devices with a variety of geometries and normal interlayers. The electrical properties of these junctions have been interpreted almost exclusively with reference to conventional proximity effect theory, which describes the behavior of low-Tc SNS devices very well. In fact, however, almost all high-Tc SNS junctions are better understood by recognizing that transport occurs through unintended pinholes in the normal interlayers. It is only recently that proximity effect theory was successfully applied to any high-Tc SNS device, despite vigorous but unsupported prior claims. The evolution of research on high-Tc SNS junctions is instructive in that it illustrates the danger inherent in assuming that device behavior can be interpreted by simply applying the most obvious theory connected with its intended structure