Interface and Related Phenomena in Josephson Junctions

Abstract

Recent studies of Josephson tunnel junctions and related fabrication techniques are reviewed. Junction development is shifting from soft superconductors of lead alloys to hard and high T_c materials such as Nb and its compounds. Tunnel barriers, as thin as several tens of angstroms, are made of the native oxide of the electrode material, of oxidized a-Si, or of a foreign metal oxide. Superconducting electrons of the electrode located in a layer within a coherence length of the interface barrier contribute to tunneling. A well-defined interface is needed to control tunneling characteristics. Control is more difficult with high T_c superconductors having short coherence lengths (≤50Å) than it is with soft superconducting materials. Avoidance of interactions with the barrier material during the fabrication process is crucial for high quality junctions.