ENHANCEMENT OF CONDUCTANCE FLUCTUATIONS IN NORMAL METALS SANDWICHED BETWEEN SUPERCONDUCTORS

Conductance fluctuations in superconductor-normal metal-superconductor junctions are studied at zero temperature. It is shown that the ampli tude of the fluctuations is no longer characterized by the universal v alue, of order of e2/h, but generally depends on the sample size and t he phase relaxation length L(phi). In the particular cases where the s ample size is much smaller than Lphi, we find that an enhancement of t he fluctuations greater than the order of e2/h can be expected to aris e. It is ascribed to a manifestation of the large fluctuation in the l evel density, which is caused by confinement of quasiparticles in the normal-metal region due to Andreev reflection.