Superconducting microbridges exhibiting Josephson properties

Abstract

In films of superconducting tin, indium and aluminium it is possible to make constrictions on a scale smaller than the coherence length over a fairly large temperature range. The ground-state Cooper pairs in and around such a microbridge give rise to properties similar to those observed in classic Josephson tunnel junctions. However, in the microbridge the normal electrons thermally excited out of the superconducting ground state may be associated with very large current densities governed by a non-equilibrium transport equation, in contrast to the situation in a Josephson tunnel junction. This nonequilibrium current is responsible for some of the unique properties of superconducting microbridges.This review describes the Josephson behaviour of superconducting microbridges in terms of the resistively shunted junction model and how this behaviour manifests itself in experiment. Most of the observed deviations from this model must be treated on the basis of non-equilibrium theories. The present knowledge of the non-equilibrium properties of superconducting microbridges is reviewed from both an experimental and theoretical point of view.

Compact tunable sub-terahertz oscillators based on Josephson junctions

“…3͑a͔͒, thus representing the non-Josephson oscillation. 8 The Josephson frequencies f J on the three arrow-marked bias points in Fig. 3͑a͒ are equal to 142.82 GHz, 143.30 GHz, and 143.58 GHz, while the observed radiation frequencies are 142.94 GHz, 143.18 GHz, and 143.25 GHz, respectively.…”

“…6,7 When Josephson junctions are strongly coupled to a resonator, self-induced steps, and non-Josephson oscillation can be observed. 8 The non-Josephson radiation was first detected in 1966 from a single point-contact Josephson junction coupled to a rectangular cavity. 9 Further theoretical investigations were performed by Auracher and Van Duzer 10 and experiments by Kanter. 11 The parametric negativeresistance effect generated by the quantum-phase-dependent inductance of the Josephson junction L J , was considered to be the explanation of the self-induced steps and of the nonJosephson oscillation.…”

“…In the latter case, the junctions will normally be underdamped with hysteretic current-voltage ͑I-V͒ characteristics. 8,11 The negative-resistance simply means the junction serves as an oscillator emitting power to the external circuits. Once the junctions are coupled to a resonator, the current induced in it will be excited and this induced current may feed back to the junctions.…”

“…We documented that the radiation frequency is shifted from the Josephson oscillation frequency f J to the resonant frequency f r , which originated the so-called non-Josephson oscillation. 8 We see promise in coupling Josephson junction arrays to modified substrates to extend this coherent radiation into the sub-THz range with higher power emitted.…”

Dynamical Properties of Quasi-One-Dimensional Conductors: A Phase Hamiltonian Approach

“…Especially they found that at T =F 0 the static conductivity is of activation type, the activation energy of which decreases linearly in proportion to the electric field. In this non-Ohmic conduction process, and also for the Ohmic conduction at T =F 0, the large local changes of 0 overcoming the potential barriers are essential (see also [144]). …”