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Two parallel stacks of coupled Josephson junctions (JJs) are investigated to clarify the physics of transitions between the rotating and oscillating states and their effect on the IV-characteristics of the system. The detailed study of phase dynamics and bias dependence of the superconducting and diffusion currents allows one to explain all features of simulated IV-characteristics and demonstrate the correspondence in their behavior. The coupling between JJ in the stacks leads to the branching of IV-characteristics and a decrease in the hysteretic region. The crucial role of the diffusion current in the formation of the IV-characteristic of the parallel stacks of coupled JJs is demonstrated. We discuss the effect of symmetry in a number of junctions in the stacks and show a decrease of the branching in the symmetrical stacks. The observed effects might be useful for development of superconducting electronic devices based on intrinsic JJs. [ABSTRACT FROM AUTHOR]

Resonance phenomena in a model of intrinsic Josephson junctions shunted by LC-elements (L-inductance, C-capacitance) are studied. The phase dynamics and IV-characteristics are investigated in detail when the Josephson frequency approaches the frequency of the resonance circuit. A realization of parametric resonance through the excitation of a longitudinal plasma wave, within the bias current interval corresponding to the resonance circuit branch, is demonstrated. It is found that the temporal dependence of the total voltage of the stack, and the voltage measured across the shunt capacitor, reflect the charging of superconducting layers, a phenomenon which might be useful as a means of detecting such charging experimentally. Thus, based on the voltage dynamics, a novel method for the determination of charging in the superconducting layers of coupled Josephson junctions is proposed. A demonstration and discussion of the influence of external electromagnetic radiation on the IV-characteristics and charge-time dependence is given. Over certain parameter ranges the radiation causes an interesting new type of temporal splitting in the charge-time oscillations within the superconducting layers. [ABSTRACT FROM AUTHOR]

The dynamics of large superwavelength open systems which are free-standing multi-wire lines with a large number of Josephson junctions, DC bias batteries and other lumped elements is analyzed using direct numerical simulation. Such systems represent the simplest version of the active Josephson antennas proposed in our earlier studies and show promise as terahertz and subterahertz radiation sources. We have studied dependences of the radiation characteristics on the antenna geometry, number of junctions, DC bias current and the lumped elements position and parameters. Detailed simulation results reveal a multitude of phase transitions between the dynamical states, which differ in the number of Josephson junctions synchronized by the excited waves of current and, hence, in the radiation power emitted into open space also as in radiation patterns. It is shown that, in the absence of noise, the Josephson antennas can emit completely coherent radiation. [ABSTRACT FROM AUTHOR]

The Shapiro effect is known, with regular steps in the voltage-current characteristic of a Josephson junction in the presence of microwave radiation, and so are its applications. In asymmetric two-junction SQUIDs (superconducting quantum interference devices), in particular the interactions between various current contributions in the two junctions lead to more varied and richer conditions. In this paper, we discuss the possibility and the impacts of a kind of internal Shapiro effect in some portions of the parameter space of the asymmetric high-TC SQUID with overdamped junctions and large loop inductance. In this predicted phenomenon, the required high-frequency radiation is produced spontaneously in the interior of the SQUID. The main message is the importance of achieving a set of nine parameters for the device whose voltage-current characteristics show no indication of spike-step-like structures. [ABSTRACT FROM AUTHOR]

In order to enhance the radiation power in the terahertz band based on intrinsic Josephson junctions of Bi2Sr2CaCu2O8+δ single crystal, we investigate a long cylindrical sample embedded in a dielectric material. Tuning the dielectric constant, the radiation power has a maximum which is achieved when it equals the dissipation caused by the Josephson plasma. This yields the optimal dielectric constant of the wrapping material in terms of the properties of a BSCCO single crystal. The maximal radiation power is found proportional to the product of the critical superconducting current squared and the typical normal resistance, which offers a guideline for choosing superconductors as a source of strong radiation. [ABSTRACT FROM AUTHOR]

Flux-flow cavity resonances in intrinsic Josephson junctions (IJJs) with long c-axis periodicity by artificial critical-current (Jc) modulation are studied numerically and theoretically. For an n-1-n-1-n-1-nIJJ system with n-layer high-Jcand one-layer low-Jcalternately stacked, numerical simulation confirms fluxon penetration only in the low-Jcjunctions under proper low magnetic fields. The simulation also shows pronounced cavity-resonance steps in the I-Vcurves of the low-Jcjunctions, meaning that fluxon dynamics can be generated under much lower magnetic fields, compared to the fields for usual IJJs with homogeneous Jc. A theoretical method for describing the flux-flow cavity-resonance properties is presented. The general disperse k-? relationship shows that, at low-kregions, the critical-current-modulated junction system can be regarded as simple homogeneous stacked junctions with a new effective thickness and a new inductive coupling strength. For general-kcases, the cavity-resonant voltage steps on the I-Vcurves at various magnetic fields can be well indexed by integers, which means excellent agreement between the theoretical analysis and the numerical simulations. [ABSTRACT FROM AUTHOR]

We present a study of the switching current distribution from the zero-voltage state to a nonzero-voltage state in Bi2Sr2CaCu2Oyintrinsic Josephson junctions. Because of a large reduction of the Josephson penetration depth attributed to an atomic-scale thickness of the superconducting layers, a thermally activated depinning of Josephson vortices was found to dominate the behaviour of the switching current distribution for mesas with lateral dimensions between 10 × 10 and 40 × 40 µm2. With decreasing lateral dimensions of the mesa, the measured switching current distribution was found to become much narrower than that in the thermally activated escape model. We argue that this behaviour is attributed to an increase in the retrapping events after an escape event. [ABSTRACT FROM AUTHOR]

In order to construct a theory for photon-assisted macroscopic quantum tunnelling (MQT) in intrinsic Josephson junctions, we revisit the model of capacitively coupled intrinsic Josephson junctions and clarify how the quantized energy levels in the N-junction stacked system distribute inside a valley of the Josephson sinusoidal potential. Furthermore, we reveal that the MQT escape rate from the single-plasmon states to the uniform voltage ones by microwave irradiation is proportional to the square of the junction number (N2) in multi-photon processes. This result is consistent with the recent finding in Bi-2212 intrinsic Josephson junctions by Jin et al2006 Phys. Rev. Lett.96177003. [ABSTRACT FROM AUTHOR]

This paper describes the effect of quenched disorder on the synchronization properties of a class of circuits known as Josephson junction arrays. The methodology extends the ‘dynamical systems approach’ used to analyze identical-element arrays to a ‘statistical mechanics approach’ to incorporate disorder, a topic of great importance from the perspective of device applications. The essential step is to map the circuit equations onto a version of the fabled Kuramoto model, whose tractability allows one to quantify the system-wide quality of synchronization. [ABSTRACT FROM AUTHOR]

This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable 2D platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given. [ABSTRACT FROM AUTHOR]

We have investigated the switching dynamics of the first and second switches in intrinsic Josephson junctions (IJJs) of Bi2Sr2CaCu2O with different maximum Josephson current density Jc to reveal the doping evolution of interaction between IJJs. For the second switch, the crossover temperature between temperature-independent switching similar to quantum tunneling and thermally activated switching is remarkably higher than that for the first switch. Moreover, slightly decreases with increasing Jc, which violates the conventional relation between the crossover temperature and the critical current density. These features can be explained not by a change in the Josephson coupling energy but by a change in the charging energy of the Josephson junction. We argue that the capacitive coupling model explains the increase in the fluctuation in the quantum regime of the second switch and the anti-correlation between and Jc. Furthermore, inductive coupling does not contribute to these peculiar phenomena in the switching dynamics of stacked IJJs. [ABSTRACT FROM AUTHOR]

We conduct microwave impedance measurements on a one-dimensional (1D) array of Josephson junctions to experimentally determine the Josephson inductance and shunt resistance of the constituent junctions. The effective Josephson energy provides an estimate of the environmental impedance, which is greatly increased due to phase fluctuations in the neighboring junctions. This enhancement is attributed to the charge solitons in the 1D system. In general, the environmental impedance is dominated by the junction’s normal resistance in the superconducting phase coherent regime, but overwhelmed by zero-bias resistance and differential resistance, respectively, in the Coulomb blockaded regime and in the phase fluctuating regime. The change in phase fluctuations owing to a dc bias agrees with the finite temperature phase diffusion model. [ABSTRACT FROM AUTHOR]

In this paper we analyze a cryogenic memory cell circuit based on a small coupled array of Josephson junctions. All the basic memory operations (e.g., write, read, and reset) are implemented on the same circuit and different junctions in the array can in principle be utilized for these operations. The presented memory operation paradigm is fundamentally different from conventional single quantum flux operation logics (SFQ). As an example, we demonstrate memory operation driven by a SFQ pulse employing an inductively coupled array of three Josephson junctions. We have chosen realistic Josephson junction parameters based on state-of-the-art fabrication capabilities and have calculated access times and access energies for basic memory cell operations. We also implemented an optimization procedure based on the simulated annealing algorithm to calculate the optimized and typical values of access times and access energies. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including high temperature superconductors, Josephson junctions, and magnetization.

We analyze the coherent dynamics of a fluxonium device (Manucharyan et al 2009 Science 326 113) formed by a superconducting ring of Josephson junctions in which strong quantum phase fluctuations are localized exclusively on a single weak element. In such a system, quantum phase tunnelling by occurring at the weak element couples the states of the ring with supercurrents circulating in opposite directions, while the rest of the ring provides an intrinsic electromagnetic environment of the qubit. Taking into account the capacitive coupling between nearest neighbors and the capacitance to the ground, we show that the homogeneous part of the ring can sustain electrodynamic modes which couple to the two levels of the flux qubit. In particular, when the number of Josephson junctions is increased, several low-energy modes can have frequencies lower than the qubit frequency. This gives rise to a quasiperiodic dynamics, which manifests itself as a decay of oscillations between the two counterpropagating current states at short times, followed by oscillation-like revivals at later times. We analyze how the system approaches such a dynamics as the ring’s length is increased and discuss possible experimental implications of this non-adiabatic regime. [ABSTRACT FROM AUTHOR]