Y. Koyama et al., MESOSCOPIC FLUCTUATIONS OF THE DC JOSEPHSON CURRENT IN A DIRTY SNS JUNCTION, Journal of the Physical Society of Japan, 66(2), 1997, pp. 430-441
We present theoretical studies on mesoscopic fluctuations of the dc Jo
sephson current in superconductor (S)-dirty normal conductor (N)-super
conductor junctions. The analytical expression for the Josephson-curre
nt fluctuation delta J(2) is obtained by using the thermal Green's fun
ction method, which is shown to he valid when the separation between t
wo superconductors is much lager than the coherence length of the dirt
y superconductor. The effects of temperature and inelastic scattering
on delta J(2) are examined. The results show that the characteristic t
emperature (size) for the reduction of delta J(2) is of the order of t
he Thouless correlation energy E(c) (the phase choherence length). Fro
m the current correlation function, the energy correlation range is es
timated to be at about E(c). In order to prepare a specific reference
for the system under our consideration, we numerically examine the cri
tical-current fluctuations delta J(c)(2) in the long-junction limit in
a model system. Numerical results show that the magnitude of delta J(
c)(2) and energy correlation range agree with our analytical result. T
he effect of the barrier potential at the NS interfaces is numerically
investigated. We find that the experimental result by Takayanagi et a
l. can be explained quantitatively within the frame work of our theory
.