1,274 research outputs found
Spontaneous Fluxoid Formation in Superconducting Loops
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 , as one would expect if
the transition took place as fast as causality permits. However, the observed
Zurek-Kibble scaling exponent 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 Josephson Tunnel Junctions: New Theory and Experiment
New scaling behavior has been both predicted and observed in the spontaneous
production of fluxons in quenched annular Josephson tunnel
junctions as a function of the quench time, . The probability
to trap a single defect during the N-S phase transition clearly follows an
allometric dependence on with a scaling exponent , 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
, 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
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
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 of the probability
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
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
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 for the production of fluxons in
annular symmetric Josephson Tunnel Junctions. We find .
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
The first-order bremsstrahlung emission spectrum is
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
where is the Bose-Einstein function. The stimulated
emission changes the spectrum to for . 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
, the spectrum is independent of and has a value
proportional to .Comment: 16 pages (plain TeX), figures available on reques
Taxonomic voucher specimens for study of post-wildfire forest habitat in Douglas County, Oregon
this publication provides data about voucher specimens deposited in the museum in conjunction with a research project on pollinators
Interactions between Cosmic Strings: An Analytical Study
We derive analytic expressions for the interaction energy between two general
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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