1,274 research outputs found

    Experimental Psychology in Relation to Insanity

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    Spontaneous Fluxoid Formation in Superconducting Loops

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    We report on the first experimental verification of the Zurek-Kibble scenario in an isolated superconducting ring over a wide parameter range. The probability of creating a single flux quantum spontaneously during the fast normal-superconducting phase transition of a wide Nb loop clearly follows an allometric dependence on the quenching time τQ\tau_{Q}, as one would expect if the transition took place as fast as causality permits. However, the observed Zurek-Kibble scaling exponent σ=0.62±0.15\sigma = 0.62\pm0.15 is two times larger than anticipated for large loops. Assuming Gaussian winding number densities we show that this doubling is well-founded for small annuli.Comment: 10 pages, 2 figures, submitted to Phys. Rev. Lett

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

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    New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched Nb−Al/Alox/NbNb-Al/Al_{ox}/Nb annular Josephson tunnel junctions as a function of the quench time, τQ\tau_{Q}. The probability f1f_{1} to trap a single defect during the N-S phase transition clearly follows an allometric dependence on τQ\tau_{Q} with a scaling exponent σ=0.5\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 σ=0.25\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

    Zurek-Kibble domain structures: The Dynamics of Spontaneous Vortex formation in Annular Josephson Tunnel Junctions

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    Phase transitions executed in a finite time show a domain structure with defects, that has been argued by Zurek and Kibble to depend in a characteristic way on the quench rate. In this letter we present an experiment to measure the Zurek-Kibble scaling exponent sigma. Using symmetric and long Josephson Tunnel Junctions, for which the predicted index is sigma = 0.25, we find sigma = 0.27 +/- 0.05. Further, there is agreement with the ZK prediction for the overall normalisation.Comment: To be published in Phys. Rev. Lett

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

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    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 BB of the probability f1ˉ\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

    Testing the Kibble-Zurek Scenario with Annular Josephson Tunnel Junctions

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    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

    New Experiments for Spontaneous Vortex Formation in Josephson Tunnel Junctions

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    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 σ\sigma for the production of fluxons in annular symmetric Josephson Tunnel Junctions. We find σ≃0.5\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.

    Suppression of Bremsstrahlung at Non-Zero Temperature

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    The first-order bremsstrahlung emission spectrum is αdω/ω\alpha d\omega/\omega at zero temperature. If the radiation is emitted into a region that contains a thermal distribution of photons, then the rate is increased by a factor 1+N(ω)1+N(\omega) where N(ω)N(\omega) is the Bose-Einstein function. The stimulated emission changes the spectrum to αTdω/ω2\alpha Td\omega/\omega^{2} for ω≪T\omega\ll T. If this were correct, an infinite amount of energy would be radiated in the low frequency modes. This unphysical result indicates a breakdown of perturbation theory. The paper computes the bremsstrahlung rate to all orders of perturbation theory, neglecting the recoil of the charged particle. When the perturbation series is summed, it has a different low-energy behavior. For ω≪αT\omega\ll\alpha T, the spectrum is independent of ω\omega and has a value proportional to dω/αTd\omega/\alpha T .Comment: 16 pages (plain TeX), figures available on reques

    Taxonomic voucher specimens for study of post-wildfire forest habitat in Douglas County, Oregon

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    this publication provides data about voucher specimens deposited in the museum in conjunction with a research project on pollinators

    Interactions between U(1)U(1) Cosmic Strings: An Analytical Study

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    We derive analytic expressions for the interaction energy between two general U(1)U(1) cosmic strings as the function of their relative orientation and the ratio of the coupling constants in the model. The results are relevant to the statistic description of strings away from critical coupling and shed some light on the mechanisms involved in string formation and the evolution of string networks.Comment: 31 pages,REVTEX, Imperial/TP/93-94/3
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