Graduate School in Nonlinear Science

Sponsored by the Danish Research Academy

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
Physics Department
University of Salerno, Italy

MIDIT-seminar 441

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.