Observation of the Little-Parks Oscillations in a System of Asymmetric Superconducting Rings

TL;DR

This study observes Little-Parks oscillations in asymmetric aluminum superconducting rings, revealing persistent current directions and potential differences without external voltage, independent of measurement current.

Contribution

It demonstrates that persistent currents in asymmetric rings can be oriented clockwise or counter-clockwise, affecting potential differences without external voltage influence.

Findings

Oscillations are independent of measurement current.

Persistent current direction can be controlled by ring asymmetry.

Potential differences occur without Faraday's voltage.

Abstract

Little-Parks oscillations are observed in a system of 110 series-connected aluminum rings 2000 nm in diameter with the use of measuring currents from 10 nA to 1000 nA. The measurements show that the amplitude and character of the oscillations are independent of the relation between the measuring current and the amplitude of the persistent current. By using asymmetric rings, it is demonstrated that the persistent current has clockwise or contra-clockwise direction. This means that the total current in one of the semi-rings may be directed against the electric field at measurement of the Little-Parks oscillations. The measurements at zero and low measuring current have revealed that the persistent current, like the conventional circulating current, causes a potential difference on the semi-rings with different cross sections in spite of the absence of the Faraday's voltage.