Quantum periodicity in the critical current of superconducting rings with asymmetric link-up of current leads

TL;DR

This study investigates the behavior of superconducting rings with asymmetric leads, revealing unexpected smooth changes in critical current near half flux quantum, challenging conventional theories and suggesting new physics.

Contribution

It provides experimental evidence of deviations from traditional theory in superconducting rings with asymmetric link-up of leads, especially near half flux quantum.

Findings

Agrees with theory near integer flux quanta

Shows smooth transition instead of jump near half flux quantum

First tantalum ring measurements suggest possible jump behavior

Abstract

We use superconducting rings with asymmetric link-up of current leads for experimental investigation of winding number change at magnetic field corresponding to the half of the flux quantum inside the ring. According to the conventional theory, the critical current of such rings should change by jump due to this change. Experimental data obtained at measurements of aluminum rings agree with theoretical prediction in magnetic flux region close to integer numbers of the flux quantum and disagree in the region close to the half of the one, where a smooth change is observed instead of the jump. First measurements of tantalum ring give a hope for the jump. Investigation of this problem may have both fundamental and practical importance.