Observation of Quantum Periodicity in the Transition Temperature of a Superconducting Cylinder

Abstract

Deaver and Fairbank1 and Doll and Nabauer2 have shown experimentally that the flax which is trapped in a superconducting cylinder is an integral multiple of the unit hc/2e. It has been pointed out3’4 that this result follows because the free energy of the superconducting state is periodic in this unit of the flux if the electrons are paired in the manner described by the Bardeen-Cooper-Schrieffer (BCS) theory.5 The free energy of the normal state, on the other hand, is virtually independent of the flux. Consequently, the transition temperature T c , which is the temperature at which the free energy of the normal and superconducting states are equal, must also be a periodic function of the enclosed flux Φ. The magnitude of the change in T c was calculated for a thin cylindrical sample using the BCS model in which the possible pairing of particles with net momentum was included.