Excess Currents in Superconducting Tunnel Junctions

Abstract

We have studied the excess currents that flow for F<Ai+A2 in two superconductor (S1-I-S2) tunnel junctions. The features of interest are "multiparticle" tunneling, which is observed as a current increase at Ai and A2, and the subharmonic effects which occur at 2A/n when Ai = A2. Strong evidence is presented that subharmonic junctions contain metallic shorts, and we show that the 2A/n series can be observed even in the absence of single-particle tunneling. By extending the study to asymmetrical junctions (Ai5^A2) we conclude that at present there is no satisfactory explanation of the subharmonic effects.

Subharmonic gap structures and Josephson effect inMgB2∕Nbmicroconstrictions

“…These resonances, due to the coupling of the gap functions at the sides of the barrier, have been mainly studied in symmetric S-I-S junctions 31,32,33,34,35,36,37,38,39 . In this case, conductance enhancements appearing at voltages V n = 2∆/n (n=1,2,3...) have been observed 40,41,42,43,44,45 . In junctions with dissimilar superconductors (S-I-S') conductance structures appear at energies (∆ S + ∆ S ′ )/m, (with m= 1,3,5...), ∆ S ′ /n and ∆ S /n (with n=1,2,3,...), depending on the energy ratio ∆ S ′ /∆ S .…”

Microwave-Photon-Assisted Tunneling in Sn-I-Sn Superconducting Tunnel Junctions

“…The resistance parameter, R=l/GNN,for each junction was determined by fitting the measured I (V') for V>2t:./e to the value of RI predicted from Eqs. (13)- (15). The o 0 value of 211 was determined using a method discussed by Rm'rell.…”

Microwave photon assisted tunneling in superconducting tunnel junctions

“…As a result, fairly sweeping assumptions and generalizations must be made before the fields can be calculated frbmEq. (34). In problems involving only the Josephson current interacting with its self-generated fields, the current is sometimes calculated by solving various linearized forms of Eq.…”

“…(18) .45--46 These methods are equivalent to solvingEq. (34) directly with the assumptions that, and that the relations between the current, voltage,and phase parameter are given by Eqs. (12) and (14).,…”