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

Abstract

It was established experimentally that a critical value of the diamagnetic current, excited by an external magnetic field in a superconducting ring (with an inductance of about $10 À6 H) with a Nb-Nb clamping point contact having the Josephson contact properties is a strictly periodic function of field strength, despite the complex microstructure of the clamping contact. The reasons of the periodic dependence are discussed on a basis of the interference model of diamagnetic current and quantized values of the circulating current in the microinterferometer formed by the clamping contact.

Measurement of energy gaps in superconductors by means of quantum interference devices

“…It should be noted that discrete changes in the current state are also observed in DCS with CPC during changes in an external magnetic field. 9 This makes it possible to measure the energy gap of superconductors using a DCS without activating it from a source of constant transport current.…”

“…9 This makes it possible to measure the energy gap of superconductors using a DCS without activating it from a source of constant transport current.…”

“…Over the last few years we have studied discrete changes in the current I 1 in the high-inductance (L ) 10 À9 H) branch of doubly-connected superconductor (DCS) with one and two clamped point contacts (CPC) [7][8][9] when a transport current I flows through the DCS. Here the short branch of the DCS is a clamped contact, through which a current I 2 (I ¼ I 1 þ I 2 ) flows.…”

“…Zimmerman and Silver 1 were the first to point out that a CPC is usually a unique miniature superconducting quantum interferometer (SQI) with several microcontacts with different critical points connected in parallel. In papers [7][8][9] dealing with a single fixed temperature (4.2 K), it is proposed that periodic discrete variations in the current I 1 in a DCS are a consequence of modulation of the critical current (I c2 ) of the CPC-SQI by the magnetic field of the variable transport current I through the DCS. This modulation is caused by quantum interference of the current I through the DCS and the current i circulating in the CPC-SQI.…”