G. Filatrella

MAGNETIC-FIELD EFFECT IN A TWO-DIMENSIONAL ARRAY OF SHORT JOSEPHSON JUNCTIONS

The effect of a constant magnetic field on the dynamics of a two‐dimensional Josephson array is studied analytically. The magnetic field induces spatially dependent states and coupling between rows, even in the absence of an external load. Numerical simulations support these conclusions.

Suppression of chaos in the perturbed sine-Gordon system by weak periodic signals

Abstract Suppression of temporal phase locked chaos in the perturbed sine-Gordon system is demonstrated by numerical simulations of the full equation in the presence of two harmonic signals. Results have been compared with a simple perturbative approach for the soliton dynamics.

Model studies of long Josephson junction arrays coupled to a high-Q resonator

Series‐biased arrays of long Josephson junction fluxon oscillators can be phase locked by mutual coupling to a high‐Q, linear distributed resonator. A simplified model of such a device, consisting of junctions described by the particle‐map perturbation theory approach which are capacitively coupled to a lumped, linear tank circuit, reproduce the essential experimental observations at a very low computational cost. A more sophisticated model, consisting of partial differential equation descriptions of the junctions, again mutually coupled to a linear tank, substantially confirm the predictions of the simplified model. In the particle‐map model, the locking range in junction bias current increases linearly with the coupling capacitance; in the partial differential equation (p.d.e.) model, this holds up to a certain maximum value of the capacitance, after which a saturation of the locking range is observed. In both models, for a given spread of junction lengths, the existence of a minimum value of the capaci...

Emission of radiation from square arrays of stacked Josephson junctions

We propose a design for two-dimensional arrays of stacked Josephson junctions and study their properties as coherent sources of radiation in the mm and sub-mm wavelength range. This design can be implemented by using either mesas of intrinsic Josephson junctions, from crystals of high TC superconductors, or artificial stacks of low TC junctions. We outline a possible Nb/AlOx/Nb trilayer fabrication process for such devices. Our model for the dynamics of the system predicts the range of parameters over which the junctions synchronize.

Experimental realization of a relativistic fluxon ratchet

We report the observation of the ratchet effect for a relativistic flux quantum trapped in an annular Josephson junction embedded in an inhomogeneous magnetic field. In such a solid state system mechanical quantities are proportional to electrical quantities, so that the ratchet effect represents the realization of a relativistic-flux-quantum-based diode. Mean static voltage response, equivalent to directed fluxon motion, is experimentally demonstrated in such a diode for deterministic current forcing both in the overdamped and in the underdamped dynamical regime. In the underdamped regime, the recently predicted phenomenon of current reversal is also recovered in our fluxon ratchet.

Linewidth calculation for bare 2D Josephson arrays

Abstract We study how disorder affects the frequency-locking properties of a bare current-biased rectangular array of Josephson junctions. Our calculation is based on a simple physical picture wherein elements within each row lock by virtue of spontaneously induced shunt currents through the transverse junctions; no locking occurs between rows. Our analytic formula for the linewidth is in excellent agreement with numerical simulations of the nonlinear circuit equations.

Flux distribution and critical currents in a one-dimensional row of a Josephson junction square lattice

Abstract We have numerically investigated the static properties of one-dimensional arrays of Josephson junctions connected in a square lattice containing a Josephson junction in each branch, accounting for self-field effects by means of self-inductances only. The static distribution of a single flux quantum and the critical current versus external magnetic field are calculated for different values of the SQUID parameter β L = 2πLI C0 Φ 0 of elementary cells. The presence of junctions in the horizontal branches significantly modifies the static properties, so that the behavior is characterized by a larger effective SQUID parameter.

Chaotic dynamics in the map model of fluxon propagation in long Josephson junctions

Abstract Chaotic dynamics in a model of a long Josephson junction (LJJ) is studied via standard techniques of non-linear maps. A characterization of chaos in such objects in terms of Lyapunov exponents and Poincare sections is given. Finally the occurrence of chaos in map dynamics is compared with preliminary results of full numerical integration of the perturbed sine-Gordon equation (PSGE).

Phase locking of fluxon oscillations in long Josephson tunnel junctions with surface losses

Abstract The influence of surface-resistance dissipation on phase locking of fluxon oscillations in long Josephson junctions of in-line geometry subjected to microwave fields which interact with the fluxon at the junction boundaries is studied by the perturbation- theory map approach and by full integration of the pde model of the junction.

Coupling of a Josephson soliton oscillator to coplanar and microstrip cavities

Abstract Experiments are reported on a Josephson soliton oscillator designed as an element of a coplanar strip resonator. We have distinguished experimentally between the effects of uniform (electric) and boundary (magnetic) coupling between the junction and the resonator. Detailed structure in the measured current-voltage characteristics and microwave response show that microstrip modes are excited by uniform coupling, while the main resonance is associated with the boundary coupled coplanar mode. Resonances internal to the junction play no role.