Contradiction between the results of observations of resistance and critical current quantum oscillations in asymmetric superconducting rings

TL;DR

This study investigates the magnetic field dependence of critical current, resistance, and rectified voltage in asymmetric and symmetric aluminum superconducting rings, revealing a contradiction between critical current oscillations and resistance measurements.

Contribution

It uncovers a contradiction between the critical current oscillations and resistance oscillations in asymmetric superconducting rings, highlighting the impact of ring asymmetry on quantum oscillation behavior.

Findings

Critical current oscillations shift by half a flux quantum in asymmetric rings.

Resistance oscillations remain at integer and half-integer flux quanta, regardless of asymmetry.

Asymmetry induces critical current anisotropy and rectification effects.

Abstract

Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings were measured in the temperature region close to the superconducting transition. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the rectification effect observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum contradict directly to the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta.