EFFECT OF THERMAL NOISE ON THE CURRENT-VOLTAGE CHARACTERISTICS OF JOSEPHSON-JUNCTIONS

We analyze the influence of thermal noise on the Shapiro steps appeari ng in the current-voltage characteristics of Josephson junctions. We s olve the Fokker-Planck equation describing the system by a path integr al method in the steepest-descent approximation, previously applied to the stochastic resonance problem. We obtain the Asymptotic Time-Perio dic Distribution P-as(phi, t), where phi epsilon [0, 2 pi] and compute from it tile voltage [phi], constructing the I-V characteristics. We find a defined ''softening'' of the Shapiro steps as temperature incre ases, for values of the system parameters in the experimentally access ible range.