Low Temp. Phys - Low Temperature Physics

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On the 50th anniversary of the Josephson effects

O. P. Balkashin

Low Temp. Phys. 38, 259 (2012); http://dx.doi.org/10.1063/1.3701716 (1 page)

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74.50.+r	Tunneling phenomena; Josephson effects
74.81.Fa	Josephson junction arrays and wire networks

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Coupled superconductors and beyond

Brian D. Josephson

Low Temp. Phys. 38, 260 (2012); http://dx.doi.org/10.1063/1.3697974 (3 pages)

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This paper describes the events leading to the discovery of coupled superconductors, the author’s move in the 1970s to a perspective where mind plays a role comparable to matter, and the remarkable hostility sometimes encountered by those who venture into unconventional areas.

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74.50.+r	Tunneling phenomena; Josephson effects
74.55.+v	Tunneling phenomena: single particle tunneling and STM

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Escape dynamics in moderately damped Josephson junctions (Review Article)

D. Massarotti, L. Longobardi, L. Galletti, D. Stornaiuolo, D. Montemurro, G. Pepe, G. Rotoli, A. Barone, and F. Tafuri

Low Temp. Phys. 38, 263 (2012); http://dx.doi.org/10.1063/1.3699625 (10 pages)

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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.

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74.50.+r	Tunneling phenomena; Josephson effects
85.25.Cp	Josephson devices
74.25.Dw	Superconductivity phase diagrams
74.25.Sv	Critical currents

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Nanoelectromechanics of superconducting weak links (Review Article)

A. V. Parafilo, I. V. Krive, R. I. Shekhter, and M. Jonson

Low Temp. Phys. 38, 273 (2012); http://dx.doi.org/10.1063/1.3699628 (10 pages)

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Nanoelectromechanical effects in superconducting weak links are considered. Three different superconducting devices are studied: (i) a single-Cooper-pair transistor, (ii) a transparent SNS junction, and (iii) a single-level quantum dot coupled to superconducting electrodes. The electromechanical coupling is due to electrostatic or magnetomotive forces acting on a movable part of the device. It is demonstrated that depending on the frequency of mechanical vibrations the electromechanical coupling could either suppress or enhance the Josephson current. Nonequilibrium effects associated with cooling of the vibrational subsystem or pumping energy into it at low bias voltages are discussed.

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07.10.Cm	Micromechanical devices and systems
85.25.Cp	Josephson devices
85.35.-p	Nanoelectronic devices
85.85.+j	Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

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Multiphoton transitions in Josephson-junction qubits (Review Article)

S. N. Shevchenko, A. N. Omelyanchouk, and E. Il’ichev

Low Temp. Phys. 38, 283 (2012); http://dx.doi.org/10.1063/1.3701717 (18 pages)

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Two basic physical models, a two-level system and a harmonic oscillator, are realized on the mesoscopic scale as coupled qubit and resonator. The realistic system includes moreover the electronics for controlling the distance between the qubit energy levels and their populations and to read out the resonator’s state, as well as the unavoidable dissipative environment. Such rich system is interesting both for the study of fundamental quantum phenomena on the mesoscopic scale and as a promising system for future electronic devices. We present recent results for the driven superconducting qubit–resonator system, where the resonator can be realized as an LC circuit or a nanomechanical resonator. Most of the results can be described by the semiclassical theory, where a qubit is treated as a quantum two-level system coupled to the classical driving field and the classical resonator. Application of this theory allows to describe many phenomena for the single and two coupled superconducting qubits, among which are the following: the equilibrium-state and weak-driving spectroscopy, Sisyphus damping and amplification, Landau–Zener–Stückelberg interferometry, the multiphoton transitions of both direct and ladder-type character, and creation of the inverse population for lasing.

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85.25.Cp	Josephson devices
85.85.+j	Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm	Micromechanical devices and systems
74.50.+r	Tunneling phenomena; Josephson effects
74.81.Fa	Josephson junction arrays and wire networks

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Superposition of states in flux qubits with a Josephson junction of the ScS type (Review Article)

V. I. Shnyrkov, A. A. Soroka, A. M. Korolev, and O. G. Turutanov

Low Temp. Phys. 38, 301 (2012); http://dx.doi.org/10.1063/1.3699781 (10 pages)

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The consequences of the transition to a quantum description of magnetic flux motion in the superconducting ring closed by an ScS type Josephson junction are considered. Here we review the principal results regarding macroscopic quantum tunneling (MQT) of Bose condensate consisting of a macroscopically large number of Cooper electron pairs. These phenomena are illustrated by the original data obtained from the study of MQT and coherent states in a modified flux qubit with energy level depletion ΔE₀₁ ≈ 2·10^–23 J (ΔE₀₁/h ≈ 30 GHz). State superposition properties in a two-well potential and the issues associated with quantum measurements of local curvature of qubits’ superposition energy levels are analyzed.

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74.50.+r	Tunneling phenomena; Josephson effects
74.25.Wx	Vortex pinning (includes mechanisms and flux creep)

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Application of SQUIDs for registration of biomagnetic signals

I. D. Voitovych, M. A. Primin, and V. N. Sosnytskyy

Low Temp. Phys. 38, 311 (2012); http://dx.doi.org/10.1063/1.3699954 (10 pages)

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Supersensitive magnetometric systems based on low-temperature SQUIDs have been designed to conduct research in cardiology (magnetocardiography) and to examine distribution of magnetic nanoparticles in biologic objects. Such SQUID magnetometric systems are distinguished by their noise immunity enabling research in nonscreened rooms. High repeatability of research outcomes has been confirmed. The use of magnetocardiographic systems has permitted a new screening information technology to be developed to diagnose heart diseases at early stages. Magnetic imaging of heart’s action currents is an ideal way to test local electrical heterogeneity of myocardium. It is shown that magnetocardiography has a significant potential for both basic science of analysis of heart’s biosignals and clinical cardiologic practice. A SQUID magnetometric system measuring magnetic signals radiated by the organs of laboratory animals is described. Information technology for automatic recording and transforming magnetometric data has been developed; the measurement of signals over rats’ livers while injecting intravenously the nanoparticles of iron oxides and lead solutions are presented.

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87.85.Ng	Biological signal processing
87.85.Pq	Biomedical imaging
87.85.Rs	Nanotechnologies-applications
85.25.Dq	Superconducting quantum interference devices (SQUIDs)
87.19.X-	Diseases

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The influence of standing waves on synchronization and self-heating of Josephson junctions in resonant systems

Alexander Grib and Paul Seidel

Low Temp. Phys. 38, 321 (2012); http://dx.doi.org/10.1063/1.3701718 (5 pages)

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We investigated numerically synchronization of Josephson junctions inside the transmission line. We have found that due to the resonance behavior of the system there appear the self-induced resonance steps, strong synchronization of junctions on these steps and the inhomogeneous distribution of the Joule heat extraction (the self heating) along the line which can lead to the formation of “hot spots” in the line. The developed model can be applied to explain recent experiments in which these effects were obtained.

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85.25.-j	Superconducting devices
85.25.Cp	Josephson devices

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dc Josephson current for d-wave superconductors with charge density waves

A. M. Gabovich and A. I. Voitenko

Low Temp. Phys. 38, 326 (2012); http://dx.doi.org/10.1063/1.3702586 (7 pages)

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dc Josephson tunnel current I_c between a d_x²₋_y²-wave superconductor and charge density waves (CDWs)—e.g. a high-T_c oxide and a conventional isotropic superconductor—was considered theoretically. Directionality of tunneling was taken into account. It was found that the dependence of I_c on the angle γ between the direction of the superconducting lobe and the plane normal to the junction is significantly altered by CDWs. For certain doping levels it may be nonmonotonic, as can be readily determined experimentally. For comparison, presented here are the corresponding results obtained for the tunnel junction between CDWs in an s-superconductor and a conventional isotropic superconductor.

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74.50.+r	Tunneling phenomena; Josephson effects
74.72.-h	Cuprate superconductors
71.45.Lr	Charge-density-wave systems
74.20.Rp	Pairing symmetries (other than s-wave)

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Josephson effect in cuprate superconducting structures

G. A. Ovsyannikov and K. Y. Constantinian

Low Temp. Phys. 38, 333 (2012); http://dx.doi.org/10.1063/1.3702585 (8 pages)

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Electron transport and microwave properties of cuprate superconducting structures (bicrystal junctions and hybrid mesa heterostructures) are discussed here. Superconducting current in junctions from cuprate superconductors with the dominant d_x²₋_y²-wave symmetry is determined by the barrier properties, characterized by the mid-gap bound states due to the multiple Andreev reflection. In bicrystal junctions it is revealed via linear dependence of critical current density on square root of the transparency, and an increase of spectral density of shot noise at low voltages are observed. The experiments demonstrate that the superconducting hybrid mesa-heterostructures have the critical current density j_с = 1–700 A/cm² for an antiferromagnetic interlayer with thickness d_M = 10–50 nm and the characteristic decay length of superconducting correlations on the order of 7 nm, due to the anomalous long range proximity effect, analyzed in the model of coupled superconductors via multilayer magnetic layer with antiferromagnetic ordering of magnetization in the layers. It is found that the hybrid mesa–heterostructures have much greater sensitivity to external magnetic field than conventional Josephson junctions because of the strong dependence of superconducting current on interlayer spin state.

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74.50.+r	Tunneling phenomena; Josephson effects
74.72.-h	Cuprate superconductors
74.25.fc	Electric and thermal conductivity
74.25.Ha	Magnetic properties including vortex structures and related phenomena
74.25.Jb	Electronic structure (photoemission, etc.)
74.25.Sv	Critical currents

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Quantization of diamagnetic current in a superconducting ring with the Josephson point contact

S. I. Bondarenko, V. P. Koverya, A. V. Krevsun, and N. M. Levchenko

Low Temp. Phys. 38, 341 (2012); http://dx.doi.org/10.1063/1.3699955 (4 pages)

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It was established experimentally that a critical value of the diamagnetic current, excited by an external magnetic field in a superconducting ring (with an inductance of about ∼10⁻⁶ H) with a Nb-Nb clamping point contact having the Josephson contact properties is a strictly periodic function of field strength, despite the complex microstructure of the clamping contact. The reasons of the periodic dependence are discussed on a basis of the interference model of diamagnetic current and quantized values of the circulating current in the microinterferometer formed by the clamping contact.

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74.50.+r

Tunneling phenomena; Josephson effects

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Transport characteristics of tunnel heterostructures: Transition from the quantum to the classical limit

V. M. Svistunov, I. V. Boylo, and M. A. Belogolovskii

Low Temp. Phys. 38, 345 (2012); http://dx.doi.org/10.1063/1.3697969 (4 pages)

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Two possible mechanisms for the partial or complete loss of information contained in the quantum-mechanical phase of an electron moving in a stochastic solid-state structure are examined. The first involves phase randomization of the electron characteristics (for example, by elastic scattering of electrons on defects in thin metallic layers) and the second arises from inelastic interactions of current carriers with external degrees of freedom. With a double-barrier heterostructure as an example, it is shown that in the first case the quantum-mechanical approach reduces to a semiclassical method, in which the probabilities of individual events appear, rather than the quantum-mechanical probability amplitudes. The second case corresponds to a transition to the classical theory of charge transport. The effect of decoherence on the differential conductivity and shot noise in double-barrier tunnelling systems with a superconducting electrode is evaluated and the changes in these owing to the transition from quantum to incoherent classical electron transport are analyzed.

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74.50.+r	Tunneling phenomena; Josephson effects
74.78.-w	Superconducting films and low-dimensional structures
74.78.Na	Mesoscopic and nanoscale systems
74.40.De	Noise and chaos
74.40.Kb	Quantum critical phenomena
73.23.-b	Electronic transport in mesoscopic systems

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Superconducting phase-dependent force in SNS junctions with mobile scatterers

A. V. Parafilo, I. V. Krive, E. N. Bogachek, and U. Landman

Low Temp. Phys. 38, 349 (2012); http://dx.doi.org/10.1063/1.3697970 (4 pages)

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We calculate the quantum (Casimir-like) superconducting phase-dependent force acting on mobile scatterers in superconductor–normal metal–superconductor (SNS) junctions. Repulsive Casimir forces are predicted in short SNS junctions with nonequilibrium (inverse) Andreev level populations. An anomalous (nonmonotonic) temperature dependence of the quantum force is found in long SNS junctions.

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74.45.+c	Proximity effects; Andreev reflection; SN and SNS junctions
03.70.+k	Theory of quantized fields

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Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures

E. M. Rudenko

Low Temp. Phys. 38, 353 (2012); http://dx.doi.org/10.1063/1.3699014 (6 pages)

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Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V ≈ 2Δ/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2Δ/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect.

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74.50.+r	Tunneling phenomena; Josephson effects
74.70.-b	Superconducting materials other than cuprates
74.20.Pq	Electronic structure calculations
74.25.Wx	Vortex pinning (includes mechanisms and flux creep)
74.25.fc	Electric and thermal conductivity

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Comparison of phase slippage processes in Josephson junctions and charge-density wave stacked junctions

Yu. I. Latyshev

Low Temp. Phys. 38, 359 (2012); http://dx.doi.org/10.1063/1.3699624 (3 pages)

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We discuss a time-space symmetry in phase slippage processes in Josephson junctions and charge density wave (CDW) stacked junctions. In Josephson junctions, above a critical current a phase slip of 2π occurs periodically in time with a period T corresponding to the rate given by the Josephson relation ν = 1/ T= 2eV/h, where V is the voltage on the junction. In CDW stacks, a CDW dislocation appears in the weakest junction of the stack when the voltage on the stack exceeds a threshold value. This phase dislocation corresponds to a local phase slippage of 2π. As the voltage is increased, new dislocations show up and form a periodic array of dislocations with period L. The inverse spacing 1/L obeys an analog of Josephson equation, v_F/L = 2eV/h.

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