Historical note: LittleParks effect 

LittleParks oscillation provides direct proof of the quantum behavior of electrons in a superconductor. In their experiments (1962), William A. Little and Roland D. Parks demonstrated that electrons forming a quantumcoherent condensate in superconducting metals exhibit sensitivity to the vectorpotential, and not only to the magnetic field, as nonquantum charged particles do. Sensitivity to the vectorpotential is a general signature of charged quantum particles related to the gauge invariance principle. Little and Parks showed that a large fraction of electrons in a superconductor behave essentially as a single quantum particle. 
LittleParks oscillation occurs in hollow superconducting cylinders pierced by a magnetic field. The critical temperature and thus the electrical resistance oscillate periodically as the magnetic field is gradually increased. The period is defined as the superconducting magnetic flux quantum h/2e divided by the area of the crosssection of the cylinder. Thus one period corresponds to an increase of the magnetic flux through the cylinder by one flux quantum h/2e. Based on quantum theory one expects that the LP oscillation of the critical temperature should occur even if the magnetic field is completely confined inside the superconducting cylinder, without entering into the walls of the cylinder. Testing this prediction experimentally is a challenging problem. 
See also images: 
 William Little, one of the discoverers of the famous LittleParks oscillations in superconductors. 
Related Links: 
W. A. Little, R. D. Parks, "Observation of quantum periodicity in the transition temperature of a superconducting cylinder," Phys. Rev. Lett. V.9, p.912 (1962)WikipediaLittleParks EffectWilliam A. LittleRonald D. Parks 




