Lattice Of Inhomogeneities Research Articles

Light bullet passing an array of carbon nanotubes with metallic mesh irregularities

We consider the propagation of 2D solitary electromagnetic waves and their scattering on a lattice of metallic inhomogeneities in the system of carbon nanotubes (CNTs). The electromagnetic field is considered on the basis of Maxwell equations, and the electronic system of carbon nanotubes is treated by the Boltzmann equation in relaxation time approximation. We numerically analyze the derived effective equation and reveal an increase of spectral composition of the last electromagnetic wave. Some possible practical applications of the discovered effect are discussed.

Stimulated ionization scattering of a wave beam forming a discharge channel in a magnetic mirror trap

The stimulated scattering of a whistler wave beam forming an extended discharge channel in a magnetic mirror trap is discovered and investigated experimentally. It is shown that the beam is scattered by relaxaction oscillations of the lattice of plasma inhomogeneities excited by the beam field. The spectrum of the pump field in the RF discharge plasma is found to broaden considerably and to contain individual modulation peaks corresponding to lattice oscillations. The peaks are observed at working gas pressures at which the electron mean free path is close to the wavelength of the standing wave forming the discharge channel. A physical model describing the phenomena observed is developed.

Ratchet behavior in nonlinear Klein-Gordon systems with pointlike inhomogeneities

We investigate the ratchet dynamics of nonlinear Klein-Gordon kinks in a periodic, asymmetric lattice of pointlike inhomogeneities. We explain the underlying rectification mechanism within a collective coordinate framework, which shows that such a system behaves as a rocking ratchet for point particles. Careful attention is given to the kink width dynamics and its role in the transport. We also analyze the robustness of our kink rocking ratchet in the presence of noise. We show that the noise activates unidirectional motion in a parameter range where such motion is not observed in the noiseless case. This is subsequently corroborated by the collective variable theory. An explanation for this phenomenon is given.

Internal resonances in periodically modulated long Josephson junctions

Current-voltage (I-V) characteristics of long Josephson junctions with a periodic lattice of localized inhomogeneities are studied. The interaction between the moving fluxons and the inhomogeneities causes resonant steps in the IV-curve. Some of these steps are due to a synchronization to resonant Fiske modes in the sub-junctions formed between the inhomogeneities. The voltage positions of the resonant steps oscillate as function of the applied magnetic field with a period corresponding to the inclusion of one magnetic flux quantum, /spl Phi//sub 0/=h/2e, per sub-junction. A qualitative explanation that takes into account the interaction between the resonance in the sub-junction and the magnetic flux density waves excited in the whole junction is given. >

Commensurability between fluxons and inhomogeneities in a long Josephson junction

Commensurability between a static fluxon chain and a periodic lattice of inhomogeneities in a long Josephson junction has been studied experimentally. Some of the equidistant peaks in the I c ( H)-curve are suppressed as predicted by the theory of Fehrenbacher et al. But, unexpectedly, a suppression of subharmonic peaks is also observed.

Commensurate fluxon states in long Josephson junctions with inhomogeneities

Measurements of the dependence of the critical current I c on the external magnetic field H in long Josephson junctions with a periodic lattice of inhomogeneities are presented. Commensurability between the lattice of inhomogeneities and the chain of fluxons induces equidistant peaks in the I c ( H)-curve. Some of these commensurability peaks are found to be suppressed as predicted by the theory of Fehrenbacher et al. which takes into account the finite width of the inhomogeneities. The suppression of the I c peaks takes place when the width of each inhomogeneity is equal to or a multiple of the spacing between the fluxons in the junction. Together with the suppression of the integer (harmonic) peaks predicted by theory, experimentally a suppression of subharmonic peaks is also observed. A qualitative explanation of this new effect is suggested.

Experimental study of fluxon dynamics in long Josephson junctions with a regular lattice of inhomogeneities

An overview of several effects experimentally observed in long quasi-one-dimensional Josephson junctions with an artificially prepared lattice of inhomogeneities is presented. An interaction of fluxons with inhomogeneities gives rise to a variety of new phenomena in Josephson junctions. A fine structure on the first zero-field step due to the radiation of a single fluxon was observed. In the large magnetic field both the effects of pinning and a multi-fluxon flux-flow were studied. In the flux-flow regime two new types of steps appeared in the IV-curves. These steps are explained in terms of Fiske steps synchronization and propagation of defects (supersolitons) in a fluxon chain.

Pinning of a fluxon chain in a long Josephson junction with a lattice of inhomogeneities: Theory and experiment

A pinning force acting upon a periodic fluxon chain in a long Josephson junction with a commensurable periodic lattice of local inhomogeneities is calculated by means of a perturbation theory. The pinning force for a single fluxon is also calculated. Dynamics of a chain and of a single fluxon are also studied. The experimental part of the paper reports results of measurements of a critical bias current Ic versus external magnetic field H. The measurements have been performed for long overlap Nb-NbOx-Pb junctions Ic(H) curve were observed at multiple values of H. Agreement between the theory and experiment for different spatial periods of the fluxon chain is satisfactory.

Superfluxons in periodically inhomogeneous long Josephson junctions.

Dynamics of a periodic array of fluxons in a dc-driven damped long Josephson junction with an installed periodic lattice of local inhomogeneities are investigated analytically by means of the perturbation theory. In the case when the array and the lattice are commensurable, the array as a whole remains in a pinned state unless the dc bias current density exceeds a certain critical value. It is demonstrated that, in the same time, stable defects in the form of a ``hole'' or surplus fluxon may propagate along the pinned array. In the long-wave approximation, an evolution equation (an ``elliptic sine-Gordon'' equation) for local deformations of the array is deduced. That equation supports exact kinklike solutions (``superfluxons'') which describe the defects mentioned. In the presence of dissipation and dc bias current (with the density smaller than critical), I-V characteristics of the junction corresponding to the motion of a superfluxon are found. The results obtained are in good agreement with results of recent numerical and physical experiments.

Super-radiant multifluxon dynamics in a system of parallel-coupled Josephson junctions.

We report experimental observation of steps in the multifluxon I-V characteristics of a long Josephson junction with a lattice of local inhomogeneities. A theoretical model of this effect based on a perturbed sine-Gordon equation is developed. We consider the super-radiant emission of plasma waves in this system and their interaction with a moving fluxon chain. The effect may also be treated as a synchronization of the Fiske oscillation modes in short junctions parallel coupled through the inhomogeneities.

“Supersoliton” excitations in inhomogeneous Josephson junctions

Multi-fluxon I-V characteristics of an annular Josephson junction with a periodic lattice of inhomogeneities have been simulated numerically in the framework of the perturbed sine-Gordon model. When the space periods of a fluxon chain and the lattice of inhomogeneities are incommensurable, resonance branches appear in I-V characteristics. These branches are supposed to be due to a new type of nonlinear excitations in Josephson junctions, which may be interpreted as solitons of the fluxon density.

Multi-fluxon dynamics in inhomogeneous Josephson junctions: experiment

Long Nb-NbO-Pb Josephson junctions with artificially formed SiO inhomogeneities in the insulator layer have been studied. A fine structure has been observed on the current-voltage characteristics of the junctions. Such structure is considered to be due to the resonant interaction between the fluxon and its radiation. The single-fluxon effect in the zero magnetic field and the multifluxon effect in a large field have been studied experimentally. The results are compared with those of the perturbation theory and numerical simulation. A multifluxon-chain pinning effect observed in the commensurable lattice of inhomogeneities is reported and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fluxon chain commensurability effect in inhomogeneity lattice

The pinning force of the fluxon chain has been studied experimentally as a function of the distance between fluxons in long Josephson junctions with artificial lattice of inhomogeneities. Sharp peaks of the critical current I c are observed at the multiple values of the external magnetic field H. This behaviour is considered as a commensurability effect of the fluxon chain in the periodic lattice of inhomogeneities.

Dynamics of a fluxon in a long Josephson junction with a periodic lattice of inhomogeneities.

A model of a damped dc-driven long Josephson junction (LJJ) with periodically installed microresistors or microshorts (microshunts), or crossed by a periodic chain of Abrikosov vortices, is considered. A maximum value of the bias current density admitting pinned states of a fluxon and a minimum value admitting free motion of fluxon are found, the latter being an important generalization of the well-known result of McLaughlin and Scott. For LJJ's with a sinusoidal profile of the inhomogeneity, a current-voltage characteristic is obtained in an explicit form.