MIDIT OFD CATS Modelling, Nonlinear Dynamics Optics and Fluid Dynamics Chaos and Turbulence Studies and Irreversible Thermodynamics Risø National Laboratory Niels Bohr Institute and Technical University of Denmark Building 128 Department of Chemistry Building 321 P.O. Box 49 University of Copenhagen DK-2800 Lyngby DK-4000 Roskilde DK-2100 Copenhagen Ø Denmark Denmark Denmark
by Giovanni Filatrella
University of Salerno, Italy
Monday February 15, 1999, 15.15 h
at MIDIT, IMM Building 305, room 027
Abstract: The inverse ac Josephson effect involves rf-induced (Shapiro) steps, i.e. the appearance of a dc voltage on the IV characteristic due to an ac drive. The standard analysis for small junctions yields a well known Bessel function dependence on the effective drive amplitude. A more recent approach, using a first order power-balance approach has allowed the extension of the threshold analysis of the so called zero-crossing steps (the steps that cross the zero current axis) also for low voltage values, while it converges to the traditional one for high voltage values. The power balance approach has proved very useful also for continuous modulated long Josephson junctions, which is well described by a perturbed sine-Gordon equation. In this case one can show that a pure ac bias current can drive a kink (in the language of josephson junctions, the fluxons) at a resonant mean velocity. Moreover, the theory can be extended also to predict the extension of the steps. Finally, we have numerically proved that in the corresponding discrete system, a lattice of the Krenkel-Kontorova type, one can eliminate the inhomogeneities because the periodic potential is given by the effective Peierls-Nabarro potential induced by the discreteness. The features of this effects have just been numerically grasped by numerical simulations, but a complete theoretical framework is still lacking.