Freezing and quantization of current passing through a doubly connected superconductor with a point contact

Abstract

The particulars of dc current passage through a structure consisting of a doubly connected superconductor (DCS) with branches that are asymmetric with respect to length and critical current have been investigated experimentally. The short branch, which has the lowest critical current, was a clamping niobium-niobium point contact with length comparable to the coherence length of the superconductor. In contrast to a previously studied DCS with a short branch much longer than the coherence length, it was found that when the short-branch current reaches the critical value the currents in the branches of the DCS do not undergo self-excited oscillations; a current exceeding the critical value enters the long branch when this current is increased in portions (is quantized), and when it is subsequently decreased it freezes partially or completely in the DCS circuit.

Quantization of diamagnetic current in a superconducting ring with the Josephson point contact

“…It is similar to that studied by us in Ref. 8, with the only difference that in the study of effect of a magnetic field on the ring a constant transport current I was not passed through the point contact. To create a magnetic field a coil with a current that generates the field H \ (not shown in Fig.…”

“…Recently, 8 in our studies at T ¼ 4.2 K upon passing a constant transport current through superconducting rings with inductance L from 10 À6 to 6 Á10 À6 H, which contain a clamping point contact with the properties of the Josephson contact, the quantization of the transport current in branches of such a ring has been found. This effect can be explained by a complex microstructure of the clamping contact which is a tiny quantum interferometer with several microcontacts of the type of S-c-S connected in parallel.…”

Current states of a doubly connected superconductor with two point contacts

“…4 when the distance between shunts is significantly larger than the coherence length of superconductors. As became apparent from comparison of results of our works, 4,5 the method of current injection into the structure plays an important role and affects the current distribution in a DCS. The magnetometer is served for contact-less measuring the magnetic field of the current flowing through the coil.…”

“…In particular, we have already found new nontrivial properties of such DCSs related to the current distribution in inductively asymmetric branches of DCSs with a local segment in one of them with reduced critical current, 4 and also in DCSs one branch of which is a clamping point contact (PC). 5 The aim of the present work is investigation of the current distribution in branches of DCSs similar to that described in Ref. 5 and containing not one but two PCs, one contact each for the branches.…”

“…5 The aim of the present work is investigation of the current distribution in branches of DCSs similar to that described in Ref. 5 and containing not one but two PCs, one contact each for the branches. The locally injected transport current can be either equal to or higher than the critical current of contacts.…”