Mesoscopic Fluctuations of the DC Josephson Current in a Dirty SNS Junction

抄録

We present theoretical studies on mesoscopicfluctuations of the dc Josephson current insuper\-conductor (S)-dirty normal conductor (N)-superconductor junctions.The analytical expression for the Josephson-currentfluctuation δ J² is obtained byusing the thermal Green's function method, which is shown to be valid when the separationbetween two superconductors is much lager thanthe coherence length of the dirty superconductor.The effects of temperature and inelasticscattering on δ J² are examined.The results show that the characteristic temperature (size)for the reduction of δ J² is of the order ofthe Thouless correlation energy E_c(the phase choherence length).From the current correlation function, the energy correlation range is estimated to be at about E_c.In order to prepare a specific referencefor the system under our consideration, we numerically examine the critical-current fluctuationsδ J²_c in the long-junction limit in a model system.Numerical results show that the magnitude ofδ J²_c and energy correlation rangeagree with our analytical result.The effect of the barrier potential at theNS interfaces is numerically investigated.We find that the experimental result by Takayanagi et al.can be explained quantitatively within the framework of our theory.