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Summary and conclusions

Description: This report presents a brief summary of the author's impressions from SQUID 91.
Date: August 1, 1991
Creator: Clarke, J.
Partner: UNT Libraries Government Documents Department
open access

Macroscopic quantum effects in the zero voltage state of the current biased Josephson junction

Description: When a weak microwave current is applied to a current-biased Josephson tunnel junction in the thermal limit the escape rate from the zero voltage state is enhanced when the microwave frequency is near the plasma frequency of the junction. The resonance curve is markedly asymmetric because of the anharmonic properties of the potential well: this behavior is well explained by a computer simulation using a resistively shunted junction model. This phenomenon of resonant activation enables one to ma… more
Date: May 1, 1985
Creator: Clarke, J.; Devoret, M. H.; Martinis, J. & Esteve, D.
Partner: UNT Libraries Government Documents Department
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Effect of the subgap conductance on the metastable states in a Josephson tunnel junction

Description: An investigation of the decay rate of metastable states in Josephson tunnel junctions in presence of thermal noise is presented. We have observed that, in the extremely underdamped regime, there is an exponential temperature dependence of the best fit value for the shunt conductance. Such a dependence shows a close relation with the temperature dependence of the subgap conductance, suggesting that the effective conductance for the escape from the metastable states obeys to a quasi-particle ther… more
Date: September 1, 1987
Creator: Cristiano, R.; Pagano, S.; Silvestrini, P.; Gray, K.E. & Liengme, O.
Partner: UNT Libraries Government Documents Department
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A Numerical Treatment of the Rf SQUID: I. General Properties andNoise Energy

Description: We investigate the characteristics and noise performance of rf Superconducting Quantum Interference Devices (SQUIDs) by solving the corresponding Langevin equations numerically and optimizing the model parameters with respect to noise energy. After introducing the basic concepts of the numerical simulations, we give a detailed discussion of the performance of the SQUID as a function of all relevant parameters. The best performance is obtained in the crossover region between the dispersive and d… more
Date: January 15, 2007
Creator: Kleiner, Reinhold; Koelle, Dieter & Clarke, John
Partner: UNT Libraries Government Documents Department
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Macroscopic quantum tunnelling in a current biased Josephson junction

Description: We discuss in this work an attempt to answer experimentally the question: do macroscopic variables obey quantum mechanics. More precisely, this experiment deals with the question of quantum-mechanical tunnelling of a macroscopic variable, a subject related to the famous Schrodinger's cat problem in the theory of measurement.
Date: November 1, 1984
Creator: Martinis, J. M.; Devoret, M. H.; Clarke, J. & Urbina, C.
Partner: UNT Libraries Government Documents Department
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Josephson oscillations of charge density waves

Description: The formation of charge density waves in solids was originally proposed as a possible mechanism for superconductivity by Froehlich. Although the experimentally discovered materials with charge density waves (CDW)s are found to have finite resistivity as a result of impurity pinning, they nevertheless reveal many interesting features including motion which is analogous to a resistively shunted Josephson junction of superconductors. The noise spectrum of CDW systems is reviewed with particular em… more
Date: January 1, 1985
Creator: Ruvalds, J. & Tua, P.F.
Partner: UNT Libraries Government Documents Department
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Superconducting demodulators, differential voltmeters, and transducers

Description: The capabilities of new superconducting measurement devices are reviewed and new applications of this technology are suggested. Specific ways in which these devices may enhance low temperature research in an orbiting laboratory are discussed. 12 refs., 2 figs.
Date: January 1, 1991
Creator: Duncan, R.V.
Partner: UNT Libraries Government Documents Department
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Nuclear magnetic resonance with dc SQUID (Super-conducting QUantum Interference Device) preamplifiers

Description: Sensitive radio-frequency (rf) amplifiers based on dc Superconducting QUantum Interface Devices (SQUIDS) are available for frequencies up to 200 MHz. At 4.2 K, the gain and noise temperature of a typical tuned amplifier are 18.6 +- 0.5 dB and 1.7 +- 0.5 K at 93 MHz. These amplifiers are being applied to a series of novel experiments on nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR). The high sensitivity of these amplifiers was demonstrated in the observation of ''nuclea… more
Date: August 1, 1988
Creator: Fan, N.Q.; Heaney, M.B.; Clark, J.; Newitt, D.; Wald, L.; Hahn, E.L. et al.
Partner: UNT Libraries Government Documents Department
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Mode-locking and the transition to chaos in dissipative systems

Description: Dissipative systems with two competing frequencies exhibit transitions to chaos. We have investigated the transition through a study of discrete maps of the circle onto itself, and by constructing and analyzing return maps of differential equations representing some physical systems. The transition is caused by interaction and overlap of mode-locked resonances and takes place at a critical line where the map losses invertibility. At this line the mode-locked intervals trace up a complete Devil'… more
Date: January 1, 1984
Creator: Bak, P.; Bohr, T. & Jensen, M.H.
Partner: UNT Libraries Government Documents Department
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Charlottesville revisited

Description: A discussion is given of the main areas of research in superconducting devices over the past eleven years. Topics discussed include SQUIDS, high frequency detectors, metrology, voltmeters, thermometers, Josephson junction switches, tunnel junctions, and refrigeration. (PMA)
Date: April 1, 1978
Creator: Clarke, J.
Partner: UNT Libraries Government Documents Department
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Microstructure and composition of a SNS Josephson junction using CaRuO{sub 3} as the metallic barrier

Description: Superconductor - normal - superconductor (SNS) edge junctions consisting of YBa{sub 2}Cu{sub 3}O{sub 7-x}/CaRuO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7-x} were fabricated on (001) LaA1O{sub 3} substrates. These devices display an excess interface resistance which is not well understood but is related to the SN interface and interlayer structure. High-resolution and conventional transmission electron microscopy were employed to investigate the SN interface to determine the structure and possible inter… more
Date: October 1, 1994
Creator: Rozeveld, S.; Merkle, K. L. & Char, K.
Partner: UNT Libraries Government Documents Department
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Effects of interlayer coupling on the magnetic and transport properties of superconducting multilayers and high-temperature superconductors

Description: The effect of interlayer coupling on the transport properties and dissipation in a magnetic field is reviewed for superconducting multilayers including highly-anisotropic high-temperature superconductors (HTS). For the applied field parallel to the superconducting layers the absence of any Lorentz-force dependence of the dissipation leads to an explanation other than flux motion. This is consistent with a Josephson junction dissipation which dominates flux motion of the insulating regions betwe… more
Date: June 1, 1994
Creator: Gray, K. E.; Hettinger, J. D. & Kim, D. H.
Partner: UNT Libraries Government Documents Department
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Research and development of superconductivity in the USA

Description: In this paper, the author focuses his attention on the present and potential applications of superconductors -- both the classic low T/sub c/ superconductors such as niobium and its alloys and the new high-T/sub c/ materials. This discussion falls naturally into two broad areas: large scale applications such as magnets and power generators, and small scale applications such as ultrasensitive detectors of electromagnetic radiation and of tiny magnetic fields;
Date: May 1, 1988
Creator: Clarke, J.
Partner: UNT Libraries Government Documents Department
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Flux lattice relaxation, noise and symmetry-breaking in frustrated Josephson junction arrays

Description: The purpose of the present report is to study: (1) Relaxation from an initially random flux state. We wish to exhibit the multiple length and time scales involved in this relaxation, and the influence of thermal fluctuations. This noisy relaxation is controlled by the dynamics of various mesoscopic ``defect`` structures defined with respect to the underlying ground-state flux structure. The defects, their mesoscopic collective patterns, and their dynamics control a complex macroscopic response,… more
Date: 1992
Creator: Gronbech-Jensen, N.; Bishop, A. R. & Lomdahl, P. S.
Partner: UNT Libraries Government Documents Department
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Quantum fluctuations of vortices in Josephson-coupled superconductors

Description: The effect of quantum fluctuations of vortices on the low temperature specific heat and reversible magnetization in the mixed state in highly anisotropic layered superconductors is discussed. For reversible magnetization, M, the change of slope in the dependence of M vs ln B, observed in Bi(2:2:1:2), is explained. In the mean, field approach this slope should be almost B independent. The specific heat due to the vortex fluctuation contribution is predicted to be linear in T at low T.
Date: March 1, 1994
Creator: Bulaevskii, L. N. & Maley, M. P.
Partner: UNT Libraries Government Documents Department
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Self-consistent solution for proximity effect and Josephson current in ballistic graphene SNS Josephson junctions

Description: We use a tight-binding Bogoliubov-de Gennes (BdG) formalism to self-consistently calculate the proximity effect, Josephson current, and local density of states in ballistic graphene SNS Josephson junctions. Both short and long junctions, with respect to the superconducting coherence length, are considered, as well as different doping levels of the graphene. We show that self-consistency does not notably change the current-phase relationship derived earlier for short junctions using the non-self… more
Date: April 6, 2010
Creator: Black-Schaffer, Annica M.
Partner: UNT Libraries Government Documents Department
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Nonlinear dynamics of domain walls and vortices in two-dimensional systems

Description: We discuss analytic and numerical studies of experimentally accessible 2-dimensional condensed matter systems which support nonlinear domain wall and vortex structures. These systems include quasi-2-dimensional magnets and 2-dimensional arrays of Josephson junctions. We emphasize the importance of these systems for investigating: complex (frustrated) ground states, dynamics (including glassy'' dynamics), interactions between domain walls and vortices, and phase transitions at finite temperature… more
Date: January 1, 1989
Creator: Bishop, A. R.
Partner: UNT Libraries Government Documents Department
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Fluctuation analysis

Description: This paper briefly reviews sources of noise in Josephson junctions, and the limits they impose on the sensitivity of dc and rf SQUIDS. The results are strictly valid only for a resistively shunted junction (RSJ) with zero capacitance, but should be applicable to point contact junctions and microbridges in so far as these devices can be approximated by the RSJ model. Fluctuations arising from Nyquist noise in the resistive shunt of a single junction are discussed in the limit eI/sub o/R/k/sub B/… more
Date: January 1, 1980
Creator: Clarke, J.
Partner: UNT Libraries Government Documents Department
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Quantum noise in Josephson junctions and squids

Description: A theory for noise in the resistively shunted Josephson junction in the quantum limit is outlined and extended to the dc SQUID. Experimental results for both the single junction and the SQUID are reported.
Date: April 1, 1981
Creator: Koch, R.H.; Van Harlingen, D.J. & Clarke, J.
Partner: UNT Libraries Government Documents Department
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Vortex lattices in theory and practice

Description: The formal simplicity of ideal point vortex systems in two dimensions has long attracted interest in both their exact solutions and in their capacity to simulate physical processes. Attention here is focused on infinite, two-fold periodic vortex arrays, including an expression for the energy density of an arbitrary vortex lattice (i.e., an arbitrary number of vortices with arbitrary strengths in a unit cell parallelogram of arbitrary shape). For the case of two vortices per unit cell, the morph… more
Date: January 1, 1988
Creator: Capmbell, Laurence J.
Partner: UNT Libraries Government Documents Department
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Coherence and chaos in extended dynamical systems

Description: Coherence, chaos, and pattern formation are characteristic elements of the nonequilibrium statistical mechanics controlling mesoscopic order and disorder in many-degree-of-freedom nonlinear dynamical systems. Competing length scales and/or time scales are the underlying microscopic driving forces for many of these aspects of ``complexity.`` We illustrate the basic concepts with some model examples of classical and quantum, ordered and disordered, nonlinear systems.
Date: December 31, 1994
Creator: Bishop, A. R.
Partner: UNT Libraries Government Documents Department
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Grain boundary microstructure and transport critical current density in YBa{sub 2}Cu{sub 3}O{sub x}

Description: It is proposed that the transport critical current (J{sub c}) density for high-{Tc} thin films, bicrystals, and bulk ceramics is determined by magnetic field penetration into the grain boundaries; the grain orientation may not in all cases be an important factor. The parameter ({lambda}{sub L}/{lambda}{sub J}){sup 2} can characterize the strength of the grain boundary coupling, which depends mainly on the crystal coherence and the structure of the boundary.
Date: September 1, 1991
Creator: Shi, Donglu, Gao, Yufei; Biondi, A. C.; Chen, J. G.; Merkle, K. L. & Goretta, K. C.
Partner: UNT Libraries Government Documents Department
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Novel processing of HTS based conductors

Description: Conductor development is one of the major long term goals in high temperature superconductor research. In this paper we report on two promising processing technologies that have been utilized to produce superconducting HTS conductors. First, melt spun YBa{sub 2}Cu{sub 3}O{sub 7} fibers rapid thermal processed for 1--8 sec at 950 to 1075{degree}C have {Tc}'s to 92 K, J{sub c}'s to 1100 A/cm{sup 2} and the orthorhombic twinned morphology typical for high quality YBa{sub 2}Cu{sub 3}O{sub… more
Date: January 1, 1990
Creator: Ginley, D. S.; Venturini, E. L.; Kwak, J. F.; Baughman, R. J.; Bourcier, R. J.; Mitchell, M. A. et al.
Partner: UNT Libraries Government Documents Department
open access

Coherence lost? Not-so-fast escapes from the in-phase attractor of a set of globally coupled nonlinear oscillators

Description: The sensitivity to noise of the coherent (or in-phase) attractor for a set of N globally coupled maps is studied; these discrete-time maps are associated with the continuous-time equations of motion for a series array of Josephson junction oscillators. We investigate both geometrical properties of the basin of attraction in the large N limit, and the implications of this geometry on the average time for the system to ``escape`` from the coherently oscillating mode. Our main results are that the… more
Date: September 1, 1993
Creator: Theiler, J. & Nichols, S.
Partner: UNT Libraries Government Documents Department
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