1,722,312 research outputs found
Depression of the interlayer Josephson coupling in Bi2Sr2CaCu2O8+x single crystals by spin-polarized current injection along the c-axis
No full textWe studied the effect of spin-injection on tunneling conduction properties of intrinsic Josephson junctions (IJJs) formed in Bi2Sr2CaCuO8+x single crystals. Properties of an identical stack (10 x 5 x 0.030 mum(3)) of IJJs were compared for the bias current injection through An and Co electrodes. Clear quasiparticle branches in tunneling current-voltage (I-V) curves from the IJJs in the stack were observed for all unpolarized bias current through the Au electrode. Spin-injection through the Co electrode caused pair breaking in the CuO2 double layers, which led to reduction of the Josephson critical current and the superconducting gap revealed in the tunneling I-V curves. (C) 2004 Published by Elsevier B.V.X115sciescopu
The phase-dependent dissipation effect in a dc SQUID
No full textThe magnetic field modulation of the voltage output of a d.c. SQUID, calculated numerically including the phase-dependent dissipation (PDD) term with a negative prefactor epsilon in Josephson junctions, exhibits maxima (minima) at integer (half-integer) values of the magnetic filling factor f in a larger bias current beyond I *, the values of which depends on the inductance parameter beta(L) and the prefactor epsilon. Asymmetry in both junction critical currents and inductances between the two branches of a d.c. SQUID loop does not change the essential feature of the magnetic-field modulation of the resistance due to the PDD effect. Copyright (C) 1996 Elsevier Science LtdX11sciescopu
Collective resonance modes of Josephson vortices in a sandwiched stack of Bi2Sr2CaCu2O8+x intrinsic Josephson junctions
No full textWe observed splitting of the low-bias vortex-flow branch in a dense-Josephson-vortex state into multiple subbranches in current-voltage characteristics of Bi2Sr2CaCu2O8+x intrinsic Josephson junctions in the long-junction limit. Each subbranch corresponds to a plasma mode in serially coupled Josephson junctions. Splitting into low-bias linear subbranches with a spread in the slopes and the intersubbranch mode-switching character are in good quantitative agreement with the prediction of the weak but finite interjunction capacitive-coupling model incorporated with the inductive coupling.open1110sciescopu
Magnetic-field-driven superconductor insulator transition in granular In/InOx films
No full textWe have measured the differential resistance of granular In/InOx films near the magnetic-field-driven superconductor-insulator (SI) transition. We observed the development of a sharp zero-bias peak in the differential resistance inside the superconducting gap in the field-driven insulating regime. We confirmed that the peak in the differential resistance originated from the Coulomb blockade of pair tunnelings between adjacent superconducting grains. Although almost full phase fluctuations are induced in a magnetic field which is far lower than the critical field of the SI transition, the global SI transition in granular systems is caused by additional phase fluctuations along with reduced pair tunnelings due to Coulomb blockade between superconducting grains.open114sciescopu
Quantitative identification of the flux-flow modes in a stack of Bi2Sr2CaCu2O intrinsic Josephson junctions
No full textWe have measured the current-voltage characteristics of Josephson vortex-flow branches (JVFB), corresponding to a highly dense Josephson vortex regime, in stacks of intrinsic Josephson junctions of Bi2Sr2CaCu2O8+x single crystals sandwiched between two An electrodes. We observed splitting of JVFB and switching between neighboring branches in the low current bias region in fields of about 4 T, with a spread in the resistivity of the branches. The result strongly indicates the existence of the resonance between the vortex lattice and collective transverse plasma modes, mediated by the inter-junction charging coupling incorporated with the strong inductive coupling.X11sciescopu
Progress in THz generation using Josephson fluxon dynamics in intrinsic junctions
No full textCollective transverse plasma modes in Bi2Sr2CaCu2O8+x, intrinsic Josephson junctions (IJJs) can be excited by the moving fluxon lattices. Progressive transformation of the standing-wave-like fluxon-lattice configuration from a triangular lattice to a rectangular lattice takes place as the dynamic fluxon-lattice modes are in resonance with the collective transverse plasma modes. In this paper, we review the progress in terahertz-firequency-range electromagnetic wave generation from the IJJs using the resonance between moving fluxon lattice and the collective transverse plasma modes.open116sciescopu
Pair charging gap observed near the magneticc-field-induced superconductor-insulator transition in granular films
No full textMeasured differential resistance (DR) of granular In/InOx films near the magnetic-field-induced superconductor-insulator (SI) transition is reported. In the field-induced transition regime a sharp zero-bias peak in the DR developed inside the superconducting (SC) gap of the grains, where time gap itself was much weakened in the field. We confirmed that the peak in the DR originated from the Coulomb blockade of pair tunnelings between adjacent grains. It strongly suggests that, in granular systems, the global SI transition is caused by fluctuations between grains as the pair tunnelings are reduced due to grain charging effect.X11sciescopu
Modeling and time delay control of shape memory alloy actuators
No full textShape memory alloy (SMA) actuators possess hard nonlinearities including backlash-like hysteresis and saturation. These nonlinearities result in steady-state error and limit-cycle problems when conventional controllers such as the proportional integral derivative (PID) are used for trajectory control. In this study, a dynamics for an SMA actuator was newly derived using the modified Liang's model. The derived dynamics showed continuity at the change of the phase transformation process, but the original model could not. SMA actuator characteristics could be well described using this dynamics. The derived dynamics could be also used effectively for the prediction of control performance and gain tuning of the time delay control (TDC). The dynamics consisted of first-order linear and second-order nonlinear equations. Accordingly, a control strategy was established for the TDC to regulate only the second-order nonlinear part for simplicity and for the internal closed loop to regulate the rest. The control strategy was examined from the point of view of influence of an anti-windup scheme and high gain tuning on control performance. An anti-windup scheme was essential to protect windup phenomenon and high gain tuning was effective when a temperature disturbance existed. In the robustness test, the TDC with high gains showed robustness to inertia variation and temperature disturbance in comparison with the TDC with low gains
Observation of Josephson-vortex-flow submodes in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions
No full textStacked intrinsic Josephson junctions form in highly anisotropic high-T-c superconductors such as Bi2Sr2CaCu2O8+x. Josephson-vortex dynamics in such systems attracts much research interests, both academic and application points of view. In a dense Josephson-vortex state (in the range of 4-5 T external magnetic field applied in parallel with the junction planes) of Bi2Sr2CaCu2O8+x stacked intrinsic Josephson junctions vortex-flow motion is in resonance with the collective plasma oscillation modes. With increasing magnetic fields beyond similar to 2 T hysteretic quasiparticle branches keep shrinking, while the collective Josephson-vortex-flow branches start appearing and become clearer. The Josephson-vortex-flow branches split into multiple sub-branches corresponding to the number of coupled junctions in the stack. The low-bias characteristics of the Josephson-vortex-flow sub-branches fit well to the inductive-capacitive hybrid coupling model. (c) 2005 Elsevier B.V. All rights reserved.X111sciescopu
Observation of a spin-singlet proximity effect in a superconductor/ferromagnet interface
No full textSince a spin-singlet superconductor (SC) and a ferromagnet (FM) have ground states with conflicting spin configurations, the superconducting order in a FM in proximity contact with a SC is bound to be suppressed. However, a rather long-range proximity effect has been observed in a metallic FM of a SC/FM junction. Recently, the possible formation of long-range spin-triplet pairing at the SC/FM interface has also been claimed. In this study, we examined the superconducting proximity effect in a simple spin-singlet SC/FM interfacial structure, where the formation of long-range spin-triplet pairing was highly unlikely. We suggest that the finite resistance reduction of the FM segment observed in this study due to the proximity contact to a SC is explicable by the ordinary short-range spin-singlet proximity effect combined with a current redistribution through the SC overlay due to the Andreev reflection at the interface of the unpolarized electrons in the FM.X111sciescopuskc
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