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

TL;DR

This study experimentally investigates how dc current passes through a doubly connected superconductor with an asymmetric branch, revealing quantization and freezing phenomena when the critical current is reached, differing from previous longer-branch cases.

Contribution

It demonstrates the effects of a short, coherence-length niobium-niobium point contact on current behavior, showing quantization and partial freezing unlike prior longer-branch DCS studies.

Findings

Currents do not oscillate when reaching critical value

Current enters the long branch in quantized portions

Partial or complete freezing of current occurs upon decreasing

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.