Fluxoid formation: size effects and non-equilibrium universality

Simple causal arguments put forward by Kibble and Zurek suggest that the scaling behaviour of condensed matter at continuous transitions is related to the familiar universality classes of the systems at quasi-equilibrium. Although proposed 25 years ago or more, it is only in the last few years that it has been possible to devise experiments from which scaling exponents can be determined and in which this scenario can be tested. In previous work, an unusually high Kibble-Zurek scaling exponent was reported for spontaneous fluxoid production in a single isolated superconducting Nb loop, albeit with low density. Using analytic approximations backed up by Langevin simulations, we argue that densities as small as these are too low to be attributable to scaling, and are conditioned by the small size of the loop. We also reflect on the physical differences between slow quenches and small rings, and derive some criteria for these differences, noting that recent work on slow quenches does not adequately explain the anomalous behaviour seen here.Comment: 7 pages, 4 figures, presentation given at CMMP 201

Retrieval cues fail to influence contextualized evaluations.

Initial evaluations generalise to new contexts, whereas counter-attitudinal evaluations are context-specific. Counter-attitudinal information may not change evaluations in new contexts because perceivers fail to retrieve counter-attitudinal cue-evaluation associations from memory outside the counter-attitudinal learning context. The current work examines whether an additional, counter-attitudinal retrieval cue can enhance the generalizability of counter-attitudinal evaluations. In four experiments, participants learned positive information about a target person, Bob, in one context, and then learned negative information about Bob in a different context. While learning the negative information, participants wore a wristband as a retrieval cue for counter-attitudinal Bob-negative associations. Participants then made speeded as well as deliberate evaluations of Bob while wearing or not wearing the wristband. Internal meta-analysis failed to find a reliable effect of the counter-attitudinal retrieval cue on speeded or deliberate evaluations, whereas the context cues influenced speeded and deliberate evaluations. Counter to predictions, counter-attitudinal retrieval cues did not disrupt the generalisation of first-learned evaluations or the context-specificity of second-learned evaluations (Experiments 2-4), but the counter-attitudinal retrieval cue did influence evaluations in the absence of context cues (Experiment 1). The current work provides initial evidence that additional counter-attitudinal retrieval cues fail to disrupt the renewal and generalizability of first-learned evaluations

Zurek-Kibble Mechanism for the Spontaneous Vortex Formation in Nb−Al/Alox/NbNb-Al/Al_{ox}/Nb Josephson Tunnel Junctions: New Theory and Experiment

New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched $Nb-Al/Al_{ox}/Nb$ annular Josephson tunnel junctions as a function of the quench time, $\tau_{Q}$. The probability $f_{1}$ to trap a single defect during the N-S phase transition clearly follows an allometric dependence on $\tau_{Q}$ with a scaling exponent $\sigma = 0.5$, as predicted from the Zurek-Kibble mechanism for {\it realistic} JTJs formed by strongly coupled superconductors. This definitive experiment replaces one reported by us earlier, in which an idealised model was used that predicted $\sigma = 0.25$, commensurate with the then much poorer data. Our experiment remains the only condensed matter experiment to date to have measured a scaling exponent with any reliability.Comment: Four pages, one figur

Spontaneous Fluxon Production in Annular Josephson Tunnel Junctions in the Presence of a Magnetic Field

We report on the spontaneous production of fluxons in the presence of a symmetry-breaking magnetic field for annular Josephson tunnel junctions during a thermal quench. The dependence on field intensity $B$ of the probability $\bar{f_1}$ to trap a single defect during the N-S phase transition drastically depends on the sample circumferences. We show that the data can be understood in the framework of the Kibble-Zurek picture of spontaneous defect formation controlled by causal bounds.Comment: Submitted to Phys. Rev. B with 5 figures on Nov. 15, 200

New Experiments for Spontaneous Vortex Formation in Josephson Tunnel Junctions

It has been argued by Zurek and Kibble that the likelihood of producing defects in a continuous phase transition depends in a characteristic way on the quench rate. In this paper we discuss an improved experiment for measuring the Zurek-Kibble scaling exponent $\sigma$ for the production of fluxons in annular symmetric Josephson Tunnel Junctions. We find $\sigma \simeq 0.5$. Further, we report accurate measurements of the junction gap voltage temperature dependence which allow for precise monitoring of the fast temperature variations during the quench.Comment: 12 pages, 5 figures, submitted to Phys. Rev.

Synchrotron Radiation Induced X-Ray Microanalysis: A Realistic Alternative for Electron- and Ion-Beam Microscopy?

Synchrotron radiation induced X-ray micro fluorescence analysis (μ-SRXRF) is compared with more conventional microanalytical techniques such as secondary ion microscopy (SIMS) and electron probe X-ray microanalysis (EPXMA) for two typical microanalytical applications. μ-SRXRF and EPXMA are employed for the analysis of individual particles, showing the complementary character of both techniques. By means of element mapping of trace constituents in a heterogeneous feldspar material, the strong and weak points of μ-SRXRF in comparison to EPXMA and SIMS are illustrated. The most striking difference between μ-SRXRF and the other two microanalytical methods is the ability of SRXRF to probe deep into the investigated material, whereas SIMS and EPXMA only investigate the upper surface of the material. The possibilities of μ-SRXRF using radiation from bending magnets of third generation synchrotron rings are briefly discussed. μ-SRXRF is considered to be a valuable method for the analysis of major, minor and trace elements which can be used profitably m parallel with electron-and ion-beam methods

Slow 4He^{4}He Quenches Produce Fuzzy, Transient Vortices

We examine the Zurek scenario for the production of vortices in quenches of liquid $^{4}He$ in the light of recent experiments. Extending our previous results to later times, we argue that short wavelength thermal fluctuations make vortices poorly defined until after the transition has occurred. Further, if and when vortices appear, it is plausible that that they will decay faster than anticipated from turbulence experiments, irrespective of quench rates.Comment: 4 pages, Revtex file, no figures Apart from a more appropriate title, this paper differs from its predecessor by including temperature, as well as pressure, quenche

Testing the Kibble-Zurek Scenario with Annular Josephson Tunnel Junctions

In parallel with Kibble's description of the onset of phase transitions in the early universe, Zurek has provided a simple picture for the onset of phase transitions in condensed matter systems, strongly supported by agreement with experiments in He3. In this letter we show how experiments with annular Josephson tunnel Junctions can and do provide further support for this scenario.Comment: Revised version with correct formula for the Swihart velocity. The results are qualitatively the same as with the previous version but differ quantitatively. 4 pages, RevTe