Violation of the Ambegaokar–Baratoff Relation in Dirty S–I–S Junctions

Abstract

It has been shown that the presence of narrow-gap quantum jumpers in “dirty” (low concentrations of identical nonmagnetic impurities in the insulator layer) superconductor–insulator–superconductor (S–I–S) junctions results in a significant deviation of the critical supercurrent (Josephson current) in the temperature range 0 ≤ T ≤ T_c (T_c is the superconducting transition temperature in the S shores of the junction) from the value given by the known Ambegaokar–Baratoff relation. It has been found that the character of this deviation changes at a certain nonzero temperature T_b < T_c: this deviation is negative at 0 ≤ T< T_b (deficiency of the supercurrent), whereas it is positive at T_b< T ≤ T_c (excess of the supercurrent). Estimates indicate that experimental manifestation of this effect can be detected.