Thermal effect in the phase-periodic conductance of disordered mesoscopic N/S structures

We report measurements of the temperature dependence of the amplitude of phase-periodic conductance oscillations in disordered (diffusive) normal metal (Ag) structures attached to a superconducting (Pb) wire at two points. The oscillation amplitude exceeds the value of e(2)/h by orders of magnitude and reaches its maximum at a temperature corresponding to the Thouless energy. The results support the recent theory of Nazarov and Stoof, [Phys. Rev. Lett. 76, 823 (1996)], which takes into account the characteristic energy dependence of the change in the diffusion coefficient of quasiparticles in a normal conductor due to Andreev reflections. The line shape of the oscillations as a function of the superconducting phase difference is found to be extremely sensitive to the quality of N/S interfaces and shows hysteretic behavior in interferometers with specially prepared clean interfaces. (C) 1996 American Institute of Physics.