Search

The vortex-vortex and vortex-antivortex interaction and energy in the planar Josephson junction arrays at extremely high density are studied. The results demonstrate that the vortex interaction is the main contributor to the energy barrier in these arrays.

We investigate the phase dynamics of moderately damped NbN/AlN/NbN Josephson junctions and we present experimental results on detailed aspects of phase diffusion processes. We measure both single escape and multiple escape and retrapping events obtaining a crossover temperature T* from Kramers to phase diffusion switching. We observe a clear dependence of the crossover temperature T* by the bias current ramp rate, while the damping factor Q remains the same. The measured effect is in strong agreement with theoretical predictions reported by Fenton and Warburton. [ABSTRACT FROM AUTHOR]

We report a systematic study of the transport properties of high critical temperature superconductor (HTS) biepitaxial Josephson junctions in the submicron range. Junction performances point to more uniform and reproducible devices and to better control of d-wave intrinsic properties. Outcomes promote novel insights into the transport mechanisms across grain boundaries and encourage further developments in the control of dissipation in HTS devices. The application of nanotechnology to HTS could be an additional tool to properly engineer the junction properties to match specific circuit design also in view of the integration into hybrid quantum circuits. [ABSTRACT FROM AUTHOR]

We demonstrate that a large area Josephson junction oscillating in the fluxon oscillator mode can be synchronized to other large junctions and simultaneously pump, by emitted radiation, a small area junction. We study the synchronization of the oscillations of the long junctions as a function of relevant experimental parameters such as bias current and stripline coupling characteristics. Experimental results obtained on coupled series arrays of Josephson junctions designed on the basis of our calculations are presented. We have fabricated coupled arrays containing each up to 1500 junctions in order to estimate the usefulness of our calculations for voltage standard devices. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which reported a simplified model of series-biased arrays of long Josephson junction fluxon oscillators. Background of studies on long Josephson junction oscillators; Overview of the model used in describing the array; Characteristics of the partial differential equation scheme used to stimulate the model.

The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e., current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities Jc. Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high-Jc junctions. These notions are universal and apply to all kinds of junctions. [ABSTRACT FROM AUTHOR]

We report on the study of the phase dynamics of high-critical-temperature superconductor Josephson junctions. We realized YBa2Cu3O7-x grain boundary biepitaxial junctions in the submicron scale using low-loss substrates and analyzed their dissipation by comparing the transport measurements with Monte Carlo simulations. The behavior of the junctions can be fitted using a model based on two quality factors, which results in a frequency-dependent damping. Moreover, our devices can be designed to have Josephson energy of the order of the Coulomb energy. In this unusual energy range, phase delocalization strongly influences the device's dynamics, promoting the transition to a quantum phase diffusion regime. We study the signatures of such a transition by combining the outcomes of Monte Carlo simulations with the analysis of the device's parameters, the critical current, and the temperature behavior of the low-voltage resistance R0. [ABSTRACT FROM AUTHOR]

The moderately damped regime in Josephson junctions (JJ) is quite common in devices characterized by low critical currents and, therefore, by low Josephson energies. Measurements of the switching current distribution (SCD) are a direct way of determining the phase dynamics in the nontrivial case of moderate damping, which is becoming more common with advances in nanopatterning superconductors and in materials science for fabricating hybrid systems. We report measurements of SCDs, in both the thermal and quantum regimes for moderately damped YBaCuO grain boundary biepitaxial JJs. A direct transition from a phase diffusion regime to macroscopic quantum tunnelling occurs at about 130 mK. The crossover to the quantum regime is determined by the magnetic field and the phase dynamics can be described by a fully consistent set of junction parameters obtained by numerical simulation. [ABSTRACT FROM AUTHOR]

Abstract: We report on measurements of the switching current probability both in the thermal and quantum regime on moderately damped NbN/MgO/NbN Josephson junctions with very low critical current density (’ 2A/cm 2). We observed three distinct regimes: below 90 mK the width of the switching distributions is constant within the experimental error, while from 90 mK to 1.6K the width increases with temperature, this change of behavior signaling the standard transition from macroscopic quantum tunneling (MQT) to thermal activation (TA) regime respectively. Above 1.6K we find effects of anti-correlation between the bath temperature and thermal fluctuations since the width of the histograms starts to collapse, and indications of a transition to a third regime called Phase Diffusion (PD) are evident, such as the change of the switching distributions symmetry. Experimental data have been analyzed through numerical fitting of the switching probability and Monte Carlo simulations, and we found a good agreement with theoretical expectations based on multiple re-trapping processes, which strongly depend on the junction damping. The parameters which completely characterize the dynamics of such moderately damped Josephson junctions have been also extracted. [Copyright &y& Elsevier]

The Josephson effect is a privileged access to the macroscopic quantum nature of superconductors. We review some ideas and experimental techniques on macroscopic quantum decay phenomena occurring in Josephson structures. The attention is mainly addressed to intermediate levels of dissipation which characterize a large majority of low critical current Josephson devices and are therefore an avoidable consequence of nanotechnology applied more and more to Josephson devices. Phase diffusion phenomena take over thermal activation in some temperature ranges also affecting the transition to macroscopic quantum tunneling, enriching the phase diagram mostly defined by the Josephson energy, the temperature and the level of dissipation. [ABSTRACT FROM AUTHOR]

The Josephson effect is a probe with unparalleled capabilities for the study of a variety of macroscopic quantum phenomena. This is a survey of important achievements and challenging trends, in particular macroscopic quantum tunneling and energy level quantization. We focus on high-TC superconducting structures and recent research on nanostructures. [ABSTRACT FROM AUTHOR]

Recent findings by G.Pepe et al. (Appl. Phys. Lett.89, 2770, 2001) have given new insights over the dynamics of Josephson junctions subject to electronic pulse injection. These experiments can be considered important steps toward the study of non-equilibrium effects involved in junctions under very fast (e.g. laser induced) pumping signals. In the governing equations (sine-Gordon or coupled sine-Gordon depending on the system) pulse operation enters via Josephson current distribution or via bias current distribution. By means of numerical simulations here we study the dependence of the switching to resistive state on fast local depression of Josephson current. Next, using simulated electronic pulse train we show how the flip-flop operating mode found in G.Pepe et al. is a common feature of single or stacked Josephson systems without regard for the pulse waveform or the presence of the gap structure in the I-V characteristics. The effect of the length and of the magnetic field is also discussed. [ABSTRACT FROM AUTHOR]

Recent considerations on the physics of YBa[sub 2]Cu[sub 3]O[sub 7-δ] films made possible explaining their transport properties as flow of supercurrents through links between the granular structure of the film. The present work deals with the analysis of the Josephson junction network as a discrete set of parallel junctions (1D array) in quasi-static conditions and is aimed to compare the results of the simulations with the experimental findings, in particular with the plateaulike features in the critical current dependence on the magnetic field. Different regimes and vortex phases have been individuated and discussed. [ABSTRACT FROM AUTHOR]

We have measured the rate of escape out of the zero-voltage state in Josephson tunnel junctions as a function of the applied magnetic field. A marked difference is found in the behaviour of long and small junctions. In all cases, the statistical distribution of the switching currents can be described using a Kramers model for the escape process, where the barrier to be overcome is the Josephson barrier and the activation energy is due to an effective temperature T/sub e/. For small junctions T/sub e/ coincides, as expected, with the thermodynamic temperature, regardless of the applied magnetic field. For long junctions instead it is found that the escape temperature depends markedly on the magnetic field and on the junction geometry (inline or overlap), suggesting a close relationship with the magnetic field distribution inside the junction. [ABSTRACT FROM PUBLISHER]

Pulse-activated transitions from the metastable to the running state and vice versa have been observed in a stacked double tunnel Nb-based Josephson system. Experimental results are compared with numerical simulations based on the Sine–Gordon model of the stacked junctions by injecting pulses with variable amplitude in one of the junctions of the stack, and observing the voltage response of the other junction. Both experimental and numerical results show the possibility to induce both direct and back-switching transitions from the metastable to the running state simply by changing the amplitude of the electronic pulses injected across the stack device. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have identified anomalous behavior of the escape rate out of the zero-voltage state in Josephson junctions with a high critical current density Jc. For this study we have employed YBa2Cu3O7−x grain boundary junctions, which span a wide range of Jc and have appropriate electrodynamical parameters. Such high Jc junctions, when hysteretic, do not switch from the superconducting to the normal state following the expected stochastic Josephson distribution, despite having standard Josephson properties such as a Fraunhofer magnetic field pattern. The switching current distributions (SCDs) are consistent with nonequilibrium dynamics taking place on a local rather than a global scale. This means that macroscopic quantum phenomena seem to be practically unattainable for high Jc junctions. We argue that SCDs are an accurate means to measure nonequilibrium effects. This transition from global to local dynamics is of relevance for all kinds of weak links, including the emergent family of nanohybrid Josephson junctions. Therefore caution should be applied in the use of such junctions in, for instance, the search for Majorana fermions. [ABSTRACT FROM AUTHOR]

Abstract: We describe the main ideas and some experimental outcomes of two experiments, both aimed to study quantum tunneling effects in high-T C structures. In the first experiment, macroscopic quantum tunneling is demonstrated in grain boundary YBaCuO Josephson junctions revealing dissipation levels lower than expected and opening novel perspectives for quantum circuitry. In the second, the low temperature dissipation is dominated by quantum tunneling of individual Pearl vortices in ultra-thin CaBaCuO systems characterized by extremely long Pearl lengths. [Copyright &y& Elsevier]