Distributed Josephson Junctions Research Articles

Design of superconducting integrated matching structures.

Superconducting integrated structures intended for matching generator impedances based on a distributed Josephson junction and detector based on a superconductor–insulator–superconductor tunnel junction in the subterahertz frequency range. The structures were modeled using the transfer matrix method. The designs were calculated in a three-dimensional numerical modeling program. A qualitative agreement was found between the results obtained by the two methods. Three designs have been designed with various topologies covering the frequency range 250...680 GHz at a level of –2 dB

Synchronization structures in the chain of rotating pendulums

The collective behavior of the ensembles of coupled nonlinear oscillator is one of the most interesting and important problems in modern nonlinear dynamics. In this paper, we study rotational dynamics, in particular space-time structures, in locally coupled identical pendulum-type elements chains that describe the behavior of phase-locked-loop systems, distributed Josephson junctions, coupled electrical machines, etc. The control parameters in the considered chains are: dissipation, coupling strength, and number of elements. In the system under consideration, the realized modes are synchronous in frequency and synchronous (in-phase) or asynchronous (out-of-phase) in phase. In the low dissipation case, the in-phase synchronous rotational regime instability region boundaries are theoretically found and the bifurcations leading to the loss of its stability are determined. The analysis was carried out for chains of arbitrary length. The existence of various out-of-phase synchronous rotational modes types is revealed: completely asynchronous in phases and the cluster in-phase synchronization regime. Regularities of transitions from one type of out-of-phase synchronous mode to another are established. It was found that at certain coupling parameter values, the coexistence of stable in-phase and out-of-phase synchronous modes is possible. It was found that for arbitrary chain length, the number of possible stable out-of-phase modes is always one less than the chain elements number. Analytical results are confirmed by numerical simulations.

Synchronization in coupled stochastic sine-Gordon wave model

The asymptotic synchronization at the level of global random attractors is investigated for a class of coupled stochastic second order in time evolution equations. The main focus is on sine-Gordon type models perturbed by additive white noise. The model describes distributed Josephson junctions. The analysis makes extensive use of the method of quasi-stability.

Synchronization in coupled second order in time infinite-dimensional models

We study asymptotic synchronization at the level of global attractors in a class of coupled second order in time models which arises in dissipative wave and elastic structure dynamics. Under some conditions we prove that this synchronization arises in the infinite coupling intensity limit and show that for identical subsystems this phenomenon appears for finite intensities. Our argument involves a method based on compensated compactness and quasi-stability estimates. As an application we consider the nonlinear Kirchhoff, Karman and Berger plate models with different types of boundary conditions. Our results can be also applied to the nonlinear wave equations in an arbitrary dimension. We consider synchronization in sine-Gordon type models which describes distributed Josephson junctions.

Excitation of Leggett Modes by Moving Josephson Vortices

Using a hydrodynamic model of multiband superconductors, we derive an equation for the dynamics of distributed Josephson junctions and analyze excitation of bulk Leggett modes by moving Josephson vortices.

Distributed Josephson Junction between Multiband Superconductors

A simple hydrodynamic model of multiband superconductors describing Leggett interband collective excitations and their interactions with electromagnetic waves is applied to description of dynamics of distributed Josephson Junction between multiband superconductors. A modified Sin-Gordon equation is obtained and excitation of Leggett modes by moving Josephson vortices is investigated.

Nanoelectronic RF Josephson Devices

Superconducting RF nanoelectronic devices exhibit a considerable potential for application in future electronics. Josephson effect based devices allow generation, detection, mixing, and parametric amplification of high-frequency signals up into the terahertz region and exhibit high sensitivity, low energy consumption, and small size. Traveling-wave devices can be realized with distributed Josephson junctions. Nonlinear lumped-element circuits can be realized that are small enough so that the circuit dynamics are governed by quantum mechanics. This allows to generate two-photon coherent states and entangled states and will open the door for quantum information processing. Nanotechnological fabrication techniques and the availability of novel materials give a strong impact on the development of novel Josephson-effect-based devices and systems. An overview over the physical principles and the possible applications of nanoelectronic RF Josephson devices is presented.

High-frequency dynamics of hybrid oxide Josephson heterostructures

We summarize our results on Josephson heterostructures Nb/Au/YBa2Cu3Ox that combine conventional (S) and oxide high-Tc superconductors with a dominant d-wave symmetry of the superconducting order parameter(D). The heterostructures were fabricated on (001) and C1 1 20) YBa2Cu3Ox films grown by pulsed laser deposition. The structural and surface studies of the (1 1 20) YBa2Cu3Ox thin films reveal nanofaceted surface structure with two facet domain orientations, which are attributed as (001) and (110)-oriented surfaces of YBa2Cu3Ox and result in S/D(001) and S/D(110) nanojunctions formed on the facets. Electrophysical properties of the Nb/Au/YBa2Cu3Ox heterostructures are investigated by the electrical and magnetic measurements at low temperatures and analyzed within the faceting scenario. The superconducting current-phase relation (CPR) of the heterostructures with finite first and second harmonics is derived from the Shapiro steps, which appear in the I-V curves of the heterostructures irradiated at frequencies up to 100 GHz. The experimental positions and amplitudes of the Shapiro steps are explained within the modified resistive Josephson junction model, where the second harmonic of the CPR and capacitance of the Josephson junctions are taken into account. We experimentally observe a crossover from a lumped to a distributed Josephson junction limit for the size of the heterostructures smaller than Josephson penetration depth. The effect is attributed to the variations of the harmonics of the superconducting CPR across the heterojunction, which may give rise to splintered vortices of magnetic flux quantum. Our investigations of parameters and phenomena that are specific for superconductors having d-wave symmetry of the superconducting order parameter may be of importance for applications such as high-frequency detectors and novel elements of a possible quantum computer.

Millimeter Wave Engineering of Distributed Josephson Junction Arrays

Josephson arrays are suitable for applications involving mm waves. Realizations of such systems typically involve structures that are large compared to the wavelength. Though many such systems are well established, there has been a shortage of generic modeling techniques, which would be simple enough for practical engineering, while quantitative. In this paper we apply the model we have recently developed to some device examples. We calculate the available output power of an array of unshunted SIS junctions. We also discuss the impact of power generation effects in Josephson voltage standards. We also extend the model to include partial synchronization. The analytic results are compared to simulated and experimental data.

Influence of fluctuations on the dynamic properties of distributed josephson junctions

Fluctuational dynamics in a long Josephson junction is studied via numerical solution of the sine-Gordon equation with allowance for the effect of white noise. It is shown that, in the case of a uniform distribution of the bias current and a constant density of the critical current, the lifetime of the superconducting state increases substantially with the junction length and tends toward a constant when a few Josephson lengths are attained.

Self-synchronization in distributed Josephson junction arrays studied using harmonic analysis and power balance

Power generation and synchronization in Josephson junction arrays have attracted attention for a long time stemming both from fundamental interest and from application potential. The authors study the array of junctions coupled to a distributed transmission line either driven by an external microwave signal or in a self-oscillating mode. The authors simplify the theoretical treatment in terms of harmonic analysis and power balance. The model explains large operation margins of superconductor-normal-superconductor and superconductor-insulator-normal-insulator-superconductor junction arrays. The authors also compare theory, experiments, and simulations of self-oscillating externally shunted superconductor-insulator-superconductor junction arrays.

Nonlocal electrodynamics of fluxons and nonlinear plasma oscillations in a distributed Josephson junction with electrodes of arbitrary thickness

We considered a distributed Josephson junction formed by superconducting plates of arbitrary thickness in the case of high critical current density when Josephson penetration depth ${\ensuremath{\lambda}}_{j}$ is less than London length ${\ensuremath{\lambda}}_{L}$. A nonlocal equation describing electrodynamics of such a junction in nondissipative approximation is derived. The soliton-like excitations of kink type (fluxons) and of breather type are studied. It is shown that the role of nonlocality is crucial for the dynamical properties of these entities: if the nonlocality is strong enough, fluxons can lose their mobility. Interactions between fluxons in the nonlocal model are studied. It is shown that for some interval of fluxon velocities and for some parameters of the junction the interactions are of solitonic type. Also the interaction may result in the emergence of a robust and long-living oscillating state of breather type. These states are studied separately using the approximation of the solution profile by one temporal Fourier harmonic.

Quantum fluctuations in a distributed Josephson junction and the spectral properties of Josephson oscillators

Within the framework of a tunneling Hamiltonian, we obtain an equation for the reduced density matrix to describe quasiclassical dynamics and fluctuation effects in distributed Josephson junctions for voltages comparable with the superconducting gap. For quasiclassical dynamics, we derive the Langevin equation describing in a self-consistent way the resistive state and fluctuations due to both the tunneling current and the electromagnetic field. Current-voltage characteristics of a Josephson oscillator are calculated in the high magnetic field approximation. The intensity and shape of the spectral line of radiation due to vortices moving in a distributed Josephson junction are found.

About Magnetic Field Distribution in Granular Superconductors

Complicated Josephson structures consisting of several distributed junctions, containing one or more common points are considered. It is analytically shown that such structures must contain an integer number of magnetic flux quanta. It is also shown that in some structures multiquantum formations are preferable. Analytical conclusions are proved by numerical experiments. It is well known, that magnetic field penetrates in type II superconductors in the form of Abrikosov’s vortices, each containing a single quantum of magnetic flux Φ0 = hc/2e = 2, 07 · 10−7 gauss · cm. Similar phenomenon is observed in distributed Josephson junctions, where external magnetic field penetrates in it in the form of vortices called Josephson vortices. Though Josephson vortices differ from Abrikosov’s ones in the set of parameters (in particular, they have no nonsuperconducting core), they also carry single magnetic flux quantum. The research of high-temperature superconductors is usually based on a model of numerous stochastically positioned Josephson junctions with random parameters (plural Josephson medium). Assuming this medium as a bidimensional analogy of a distributed junction, the magnetic field also penetrates in it in the form of vortices called “hypervortices” and its structure has not been researched in details. Furthermore, the magnetic flux of the hypervortex is assumed now to be equal to Φ0. In this paper the distributed Josephson junction’s structure is being considered as a system, formed by several (N) half-infinite distibuted junctions with one common point ( the ”Star” topol-ogy), as shown on Figure 1. Figure 1: Several half-infinite junctions withone common point. Let common point has coordinate x = 0 for all junctions, the phase difference of the order parameter in each junction is counted clockwise, and the points of each junction have positive coordinates x ≥ 0. In each junction φ(x, t) is given by equation: ∂φ (x, t) ∂x2 − γ ∂φ (x, t) ∂t − ∂ φ (x, t) ∂t2 = sinφ (x, t) (1) where x and t are dimensionless (normalized) coordinate and time, γ – dimensionless dissipation parameter, due to junctions ohmic resistance. The normalized magnetic field in junction is determined by relation h (x, t) = ∂φ (x, t)/∂x. For infinite junction there are isolated solutions [2] φ0 (x) = 4 arctg e , the Josephson magnetic vortex given by h0 (x) = dφ0 (x)/dx = 4e x /( 1 + e ) and the value of it’s magnetic flux is Progress In Electromagnetics Research Symposium 2005, Hangzhou, China, August 22-26 409

Phase-sensitive evidence for a predominant d-wave pairing symmetry in the electron doped superconductor La 2− xCe xCuO 4− y

We have performed a phase-sensitive test of the symmetry of the superconducting order parameter of the electron doped cuprate La 2− x Ce x CuO 4− y using a superconducting quantum interferometer with spatially distributed Josephson junctions. The magnetic field dependence of the critical current gives strong evidence for a predominant d x 2− y 2 (d-wave) symmetry of the superconducting order parameter of the particular sample measured. It also gives upper limits for the s wave component in a mixed order parameter of the type s+ id.

Averaged equations for distributed Josephson junction arrays

We use an averaging method to study the dynamics of a transmission line studded by Josephson junctions. The averaged system is used as a springboard for studying experimental strategies which rely on spatial non-uniformity to achieve enhanced synchronization. A reduced model for the near resonant case elucidates in physical terms the key to achieving stable synchronized dynamics.

Magnetic-field dependence of the maximum supercurrent of La2-xCexCuO4-y interferometers: evidence for a predominant dx2-y2 superconducting order parameter.

We performed a phase-sensitive test of the symmetry of the superconducting order parameter of the electron doped cuprate La(2-x)Ce(x)CuO(4-y) using a superconducting quantum interferometer with spatially distributed Josephson junctions. The studies were made on a thin film grown on a SrTiO3 tetracrystal substrate. The superconducting transition temperature was about 29 K which indicates that the sample is close to optimal doping. The magnetic field dependence of the critical current gives strong evidence for a predominant dx(2)(-y(2)) order parameter symmetry of the sample measured. It also gives upper limits for the s-wave component in a mixed order parameter of the type s+idx(2)(-y(2)).

Nonlinear ac resistivity in s-wave and d-wave disordered granular superconductors.

We model s-wave and d-wave disordered granular superconductors with a three-dimensional lattice of randomly distributed Josephson junctions. The nonlinear ac resistivity rho(2) of these systems was calculated using Langevin dynamical equations. The current amplitude dependence of rho(2) at the peak position is found to be a power law characterized by exponent alpha, which is not universal but depends on the self-inductance and current regimes. In the weak current regime alpha is independent of the self-inductance and alpha = 0.5+/-0.1 for both s- and d-wave materials. In accord with experiments, we find alpha approximately 1 for some interval of inductance in the strong current regime.

Microwave absorption ins- andd-wave disordered superconductors

We model s- and d-wave ceramic superconductors with a three-dimensional lattice of randomly distributed Josephson junctions with finite self-inductance. The field and temperature dependences of the microwave absoption are obtained by solving the corresponding Langevin dynamical equations. We find that at magnetic field H=0 the microwave absoption of the s-wave samples, when plotted against the field, has a minimum at any temperature. In the case of d-wave superconductors one has a peak at H=0 in the temperature region where the paramagnetic Meissner effect is observable. These results agree with experiments. The dependence of the microwave absorption on the screening strength was found to be nontrivial due to the crossover from the weak to the strong screening regime.

Pipelined DC-powered SFQ RAM

We present the design and test results of components for a superconductor Cryogenic Random Access Memory (CRAM). The 16-Kb RAM design consists of four 4-Kb sub-arrays (blocks) with a 400 ps access time (latency) and a 100 ps cycle time (throughput). Each 4-Kb RAM block comprises a row-accessed 32/spl times/128 memory cell array, bipolar line drivers, row decoders, and column sense circuits. The implementation of specially designed distributed Josephson junctions in the sensing circuits reduces the overall size of the blocks and allows the use of smaller dc control currents.