Two permitted states of superconducting ring observed at measurements of its critical current

TL;DR

This study investigates the magnetic flux dependence of critical current in aluminium superconducting rings, revealing a single permitted state in uniform rings and two states in rings with a narrow spot, due to spectral discreteness.

Contribution

It demonstrates the existence of two permitted states in superconducting rings with a narrow spot, expanding understanding of flux quantization effects.

Findings

Single permitted state observed in homogeneous rings

Two permitted states observed in rings with a narrow spot

Spectral discreteness influences the number of permitted states

Abstract

Magnetic dependencies of the critical current of superconducting, aluminium rings, with homogeneous section and with small narrow spot, are measured. Only permitted state at each magnetic flux value is observed in the conventional ring because of strong discreteness of its spectrum. But two states are observed because of the small narrow spot.