Phase-periodic proximity-effect compensation in symmetric normal/superconducting mesoscopic structures

The conductance (G) of mirror-symmetric, disordered normal (N) metal mesoscopic structures with two interfaces to superconductors (S) has been studied experimentally with applied condensate phase differences Delta phi between the N/S interfaces. At Delta phi = 2n pi(n = 0,1,2,3,...) the conductance showed reentrance to the normal state below the temperature corresponding to the Thouless energy. The current-voltage characteristics were found to be: strongly nonlinear even at distances between the N/S interfaces largely exceeding the normal-metal coherence length. An influence of superconductors almost completely disappeared at Delta phi = (2n + 1) pi where the structures showed normal behavior. Calculations based on a quasiclassical theory have been performed offering a quantitative explanation of such a phase-periodic reentrance. The value of the superconducting gap Delta(eff) at the Ag/Al interface has been obtained. We find that Delta(eff)(T,V-->0) = beta .Delta(BCS)(T) with beta = 0.2 independent of temperature in the temperature interval of 0.1 K < T < 1.6 K; Delta(BCS)(T) is the BCS gap vs T function in Al. [S0163-1829(98)01746-9].