Could two degenerate energy states be observed for a superconducting ring at $\Phi_{0}$/2?

TL;DR

This paper provides experimental evidence of two degenerate energy states in asymmetric superconducting aluminum rings at half the flux quantum, using resistance and voltage oscillations, with some conflicting results from critical current measurements.

Contribution

It demonstrates the observation of degenerate energy states at $rac{ ext{Φ}_0}{2}$ through multiple quantum oscillation measurements in asymmetric superconducting rings.

Findings

Evidence of two degenerate energy states at $rac{ ext{Φ}_0}{2}$ from resistance and voltage oscillations.

Quantum oscillations of critical current show periodical dependence on magnetic flux.

Contradictions between Little-Parks oscillations and critical current measurements are observed.

Abstract

The Little-Parks oscillations of the resistance and the quantum oscillations of the rectified voltage observed for asymmetric superconducting Al rings give experimental evidence of two degenerate energy states at the magnetic flux $\Phi_{0}$/2. The quantum oscillations of the critical current as a function of magnetic field have also been measured. On the one hand, these oscillations confirm that the quantum oscillations of the rectified voltage are a consequence of periodical dependence of the asymmetry of the current-voltage curves and, on the other hand, comparison of the oscillations with Little-Parks measurements results in contradiction.