Conductance fluctuations in a superconductor-dirty normal conductor-superconductor junction

We obtain an analytical expression for the conductance fluctuation in a sup erconductor-dirty normal conductor-superconductor (SNS) junction using the Green's function method. It is shown that the magnitude of the fluctuation is enhanced by a factor of (L-phi/L-x)((4-d)/2) compared with the universal value of the order of e(2)/h, (L phi: the phase coherence length, L-x: the separation between two superconductors, d: the effective dimension of the normal region). It is also shown that the energy correlation range is of th e order of the inverse of the phase relaxation time, in contrast to ordinar y cases where the energy correlation range is of the order of the Thouless energy We calculate the phase coherence length L phi as a function of the s ample size and find that L phi becomes longer with the reduction of the sam ple size. This indicates that the conductance fluctuation in an SNS junctio n can be strongly enhanced beyond the universal value.