Flux sensitivity of a piecewise normal and superconducting metal loop

We consider a loop composed of a superconducting segment and a normal segment with an Aharonov-Bohm flux through the hole of the loop. The normal segment is assumed to be long compared to the superconducting coherence length but short compared to a mean inelastic diffusion length. The elementary excitation spectrum of the ground state of this loop is periodic with period hc/2e as long as the superconducting segment is larger than. If the superconducting segment length becomes of the order of , quasiparticles can tunnel through the superconducting gap and give rise to an excitation spectrum which is periodic with period hc/e.. AE © 1986 The American Physical Society.