Experimental investigations of the change with magnetic flux of quantum   number in superconducting ring
  The magnetic dependencies of the critical current of aluminum ring with asymmetric link-up of current leads have been measured in order to clear up the essence of the paradoxical absence of the jump of the critical current at the quantum number change revealed before at the measurements of asymmetric superconducting ring. The measurements have shown that the experimental and theoretical dependencies agree in the region of magnetic field corresponding to integer numbers of the flux quantum and disagree at the half of the flux quantum. The jump is not observed as well as in the asymmetric rings. 
A.V. Burlakov, V.L. Gurtovoi, A.I. Ilin, A.V. Nikulov, and V.A. Tulin
cond-mat.supr-con quant-ph