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The induced motion of vortex chains (helical waves) is studied in a system consisting of a Josephson Junction coupled magnetically to a waveguide. The relation between the transport current density and the chain velocity is established.
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Collective pinning phenomena of vortices in Josephson junction networks (JJN) in magnetic fields are studied using numerical simulations. We consider two kinds of structure of JJN: a ladder (Josephson junction ladder, JJL) and a t...
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Collective pinning phenomena of vortices in Josephson junction networks (JJN) in magnetic fields are studied using numerical simulations. We consider two kinds of structure of JJN: a ladder (Josephson junction ladder, JJL) and a two-dimensional square array (Josephson junction array, JJA). For the JJL and JJA with distribution of the strengths of junction critical currents, we investigate the critical current of vortex depinning in the presence of bias currents. On the basis of a theory of collective vortex pinning, it is found that the critical currents for both JJL and JJA show a universal scaling behavior.
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This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and ...
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This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and turbulence intensity (T.I.) influence the wing-junction flow was also studied. The junction-flow structures at low Reynolds numbers were visualized using the smoke-wire technique. The smoke-streak flow patterns were classified into two characteristic modes - horseshoe vortex and non-horseshoe vortex. The horseshoe-vortex patterns were further categorized as the junction-vortex mode and non-junction-vortex mode. The velocity vectors were measured using the particle-image velocimetry (PIV), and the data was utilized to calculate the junction vorticity (Ω). Experimental results indicate that the straight wing has the maximum junction vorticity. The Ω decreases with increasing α and Λ and with decreasing Re. The Ω decreases with increasing T.I. The upstream T.I. generated by the mesh fences was more significant than that produced by sandpapers.
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It is shown that a vortex trapped in one of the banks of a planar edge-type Josephson junction in a narrow thin-film superconducting strip can change drastically the dependence of the junction critical current on the applied field...
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It is shown that a vortex trapped in one of the banks of a planar edge-type Josephson junction in a narrow thin-film superconducting strip can change drastically the dependence of the junction critical current on the applied field, I_(H). When the vortex is placed at certain discrete positions in the strip middle, the pattern I_c(H) has zero at H=0 instead of the traditional maximum of '0-type' junctions. The number of these positions is equal to the number of vortices trapped at the same location. When the junction-vortex separation exceeds ~ W, the strip width, I_c(H) is no longer sensitive to the vortex presence. The same is true for any separation if the vortex approaches the strip edges.
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We study the propagation properties of a single vortex in square Josephson-junction arrays (JJA) with free boundaries and subjected to an applied dc current. We model the dynamics of the JJA by the resistively and capacitively shu...
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We study the propagation properties of a single vortex in square Josephson-junction arrays (JJA) with free boundaries and subjected to an applied dc current. We model the dynamics of the JJA by the resistively and capacitively shunted junction equations. For zero Stewart-McCumber parameter beta(c) we find that the vortex always escapes from the array when it gets to the boundary. For beta(c) greater than or equal to 2.5 and for low currents we find that the vortex escapes, while for larger currents the vortex is reflected as an antivortex at one edge and the antivortex as a vortex at the other, leading to a stationary vortex oscillatory state and to a nonzero time-averaged voltage. The escape and the reflection of a vortex at the array edges is qualitatively explained in terms of a coarse grained model of a vortex; interacting logarithmically with its image. For beta(c) greater than or equal to 50 we find that the reflection regime is split up in two disconnected regimes separated by a second vortex escape regime. When considering an explicit vortex-antivortex pair in an array with periodic boundaries, we find a solitonlike nondestructive collision in virtually the same current regimes as where we find reflection of a. single vortex at a free boundary; outside these current regimes the pair annihilates. We also discuss the case when the free boundaries are at 45 degrees with respect to the current direction, and thus the angle of incidence of the vortex to the boundaries is 45 degrees. Finally, we study the effect of self-induced magnetic fields (for penetration depths ranging from 10 to 0.3 times the lattice spacing) by taking into account the full-range inductance matrix of the array and find qualitatively equivalent results. We also discuss possible consequences of these results to experimental systems. [References: 35]
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When a soliton propagates in a discrete lattice it excites small-amplitude linear waves in its wake. In a dc current-biased Josephson-junction (JJ) array these manifest as electromagnetic(EM) waves excited by a (magnetic field ind...
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When a soliton propagates in a discrete lattice it excites small-amplitude linear waves in its wake. In a dc current-biased Josephson-junction (JJ) array these manifest as electromagnetic(EM) waves excited by a (magnetic field induced) chain of propagating magnetic vortices. When the vortex velocity and the phase velocity of one of the excited EM waves match, phase-locking occurs. This produces resonant steps in the current-voltage characteristics where amplification of EM radiation occurs. We report the first observation of phase-locking-induced amplification of EM radiation at 77 K and above in JJ arrays made of high temperature superconductors.
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Current-driven dynamics of superconducting phases of Josephson junction networks in magnetic fields are studied numerically. We here consider two-dimensional arrays (Josephson junction arrays, JJAs) with positional disorder. In th...
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Current-driven dynamics of superconducting phases of Josephson junction networks in magnetic fields are studied numerically. We here consider two-dimensional arrays (Josephson junction arrays, JJAs) with positional disorder. In the presence of strong disorder and driving bias currents, the nucleation of vortex-antivortex pairs causes the plastic flow and elastic flow of phases in JJAs. We focus on two threshold currents that characterize the boundaries of these flow regimes. We analyze the threshold currents on the basis of the scaling theory of pinning due to random potentials. It is found that the threshold currents show scaling behaviors characterized by scaling exponents in one dimension.
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It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity excee...
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It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric. (c) 2007 Elsevier B.V. All rights reserved.
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We have studied numerically the motion of vortices in an underdamped Josephson junction array, especially in the presence of a magnetic field of 1/5 flux quantum per plaquette. Such a magnetic field density provides a square vorte...
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We have studied numerically the motion of vortices in an underdamped Josephson junction array, especially in the presence of a magnetic field of 1/5 flux quantum per plaquette. Such a magnetic field density provides a square vortex lattice that has a lattice constant of root 5a, where a is the plaquette length of the array. For a ratchet array, we use both alternate critical currents and alternate inter-capacitances along the direction of vortex flow. To analyze the dynamics of several vortices around a mid row of the array, we use the time-dependent vorticity-vorticity correlation function as well as the time-dependent vorticity. The vortices on a fractional Shapiro n/5-step are found to move through n plaquettes transversely to the direction of the applied current during a single ac cycle.
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We study the zero-temperature phase transitions of two-dimensional superconducting arrays with both the self- and the junction capacitances in the presence of external magnetic fields. We consider two kinds of excitations from the...
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We study the zero-temperature phase transitions of two-dimensional superconducting arrays with both the self- and the junction capacitances in the presence of external magnetic fields. We consider two kinds of excitations from the Mott insulating phase, charge-dipole excitations and single-charge excitations, and apply the second-order perturbation theory to find their energies. The resulting phase boundaries are found to depend strongly on the magnetic frustration, which measures the commensurate-incommensurate effects. Comparison of the obtained values with those in recent experiment suggests the possibility that the superconductor-insulator transition observed in experiment may not be of the Berezinskii-Kosterlitz-Thouless type. The system is also transformed to a classical three-dimensional XY model with the magnetic field in the time direction; this allows the analogy to bulk superconductors, revealing the nature of the phase transitions. [S0163-1829(98)01645-2]. [References: 27]
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