Supercurrents through barriers

TLDR

Superconducting systems partitioned by thin barriers that allow supercurrents are discussed, highlighting analogies with other phase‑coherent processes. The study develops and applies a phenomenological theory to explore how superconducting long‑range order affects supercurrents across thin barriers, including magnetic field penetration, interference, wave‑propagation cut‑off, a.c. currents, and microwave‑induced d.c. I‑V structure.

Abstract

Abstract Superconducting systems partitioned by barriers which are thin enough to allow supercurrents to pass through them are discussed. The implications for such systems of superconducting long-range order are considered, and a phenomenological theory developed and applied to a number of topics: penetration of a magnetic field into a barrier, interference of supercurrents in the presence of a magnetic field, the cut-off frequency associated with the propagation of electromagnetic waves along a barrier, a.c. supercurrents, and structure in the d.c. current-voltage characteristics of a barrier resulting from an applied microwave field or the a.c. supercurrent. The phenomenological theory is justified by the use of microscopic theory, and a new approach, based on the Gor'kov method, is described. The results of this approach, which is of more general validity than the tunnelling Hamiltonian method, are shown to be expressible in terms of Feynman diagrams. Attention is drawn to the analogy between supercurrents and other processes involving phase coherence.