1,143 research outputs found
Vortex Entanglement and Broken Symmetry
Based on the London approximation, we investigate numerically the stability
of the elementary configurations of entanglement, the twisted-pair and the
twisted-triplet, in the vortex-lattice and -liquid phases. We find that, except
for the dilute limit, the twisted-pair is unstable and hence irrelevant in the
discussion of entanglement. In the lattice phase the twisted-triplet
constitutes a metastable, confined configuration of high energy. Loss of
lattice symmetry upon melting leads to deconfinement and the twisted-triplet
turns into a low-energy helical configuration.Comment: 4 pages, RevTex, 2 figures on reques
Experimental study of electric breakdowns in liquid argon at centimeter scale
In this paper we present results on measurements of the dielectric strength
of liquid argon near its boiling point and cathode-anode distances in the range
of 0.1 mm to 40 mm with spherical cathode and plane anode. We show that at such
distances the applied electric field at which breakdowns occur is as low as 40
kV/cm. Flash-overs across the ribbed dielectric of the high voltage
feed-through are observed for a length of 300 mm starting from a voltage of 55
kV. These results contribute to set reference for the breakdown-free design of
ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC)
Casimir Force between Vortex Matter in Anisotropic and Layered Superconductors
We present a new approach to calculate the attractive long range
vortex-vortex interaction of the van der Waals type present in anisotropic and
layered superconductors. The mapping of the statistical mechanics of vortex
lines onto the imaginary time quantum mechanics of two dimensional charged
bosons allows us to define a 2D Casimir problem: Two half-spaces of (dilute)
vortex matter separated by a gap of width R are mapped to two dielectric
half-planes of charged bosons interacting via a massive gauge field. We
determine the attractive Casimir force between the two half-planes and show,
that it agrees with the pairwise summation of the van der Waals force between
vortices previously found by Blatter and Geshkenbein [Phys. Rev. Lett. 77, 4958
(1996)]Comment: 11 pages, 3 figure
On the Electric Breakdown in Liquid Argon at Centimeter Scale
We present a study on the dependence of electric breakdown discharge
properties on electrode geometry and the breakdown field in liquid argon near
its boiling point. The measurements were performed with a spherical cathode and
a planar anode at distances ranging from 0.1 mm to 10.0 mm. A detailed study of
the time evolution of the breakdown volt-ampere characteristics was performed
for the first time. It revealed a slow streamer development phase in the
discharge. The results of a spectroscopic study of the visible light emission
of the breakdowns complement the measurements. The light emission from the
initial phase of the discharge is attributed to electro-luminescence of liquid
argon following a current of drifting electrons. These results contribute to
set benchmarks for breakdown-safe design of ionization detectors, such as
Liquid Argon Time Projection Chambers (LAr TPC).Comment: Minor revision according to editor report. 17 pages, 15 figures, 2
tables. Turboencabulato
Dynamics and stability of vortex-antivortex fronts in type II superconductors
The dynamics of vortices in type II superconductors exhibit a variety of
patterns whose origin is poorly understood. This is partly due to the
nonlinearity of the vortex mobility which gives rise to singular behavior in
the vortex densities. Such singular behavior complicates the application of
standard linear stability analysis. In this paper, as a first step towards
dealing with these dynamical phenomena, we analyze the dynamical stability of a
front between vortices and antivortices. In particular we focus on the question
of whether an instability of the vortex front can occur in the absence of a
coupling to the temperature. Borrowing ideas developed for singular bacterial
growth fronts, we perform an explicit linear stability analysis which shows
that, for sufficiently large front velocities and in the absence of coupling to
the temperature, such vortex fronts are stable even in the presence of in-plane
anisotropy. This result differs from previous conclusions drawn on the basis of
approximate calculations for stationary fronts. As our method extends to more
complicated models, which could include coupling to the temperature or to other
fields, it provides the basis for a more systematic stability analysis of
nonlinear vortex front dynamics.Comment: 13 pages, 8 figure
Thermal Suppression of Strong Pinning
We study vortex pinning in layered type-II superconductors in the presence of
uncorrelated disorder for decoupled layers. Introducing the new concept of
variable-range thermal smoothing, we describe the interplay between strong
pinning and thermal fluctuations. We discuss the appearance and analyze the
evolution in temperature of two distinct non-linear features in the
current-voltage characteristics. We show how the combination of layering and
electromagnetic interactions leads to a sharp jump in the critical current for
the onset of glassy response as a function of temperature.Comment: LaTeX 2.09, 4 pages, 2 figures, submitted to Phys. Rev. Let
On the theory of diamagnetism in granular superconductors
We study a highly disordered network of superconducting granules linked by
weak Josephson junctions in magnetic field and develop a mean field theory for
this problem. The diamagnetic response to a slow {\it variations} of magnetic
field is found to be analogous to the response of a type-II superconductor with
extremely strong pinning. We calculate an effective penetration depth
and critical current and find that both and
are non-zero but are strongly suppressed by frustration.Comment: REVTEX, 12 pages, two Postscript figure
Lower critical field H_c1 and barriers for vortex entry in Bi_2Sr_2CaCu_2O_{8+delta} crystals
The penetration field H_p of Bi_2Sr_2CaCu_2O_{8+delta} crystals is determined
from magnetization curves for different field sweep rates dH/dt and
temperatures. The obtained results are consistent with theoretical reports in
the literature about vortex creep over surface and geometrical barriers. The
frequently observed low-temperature upturn of H_p is shown to be related to
metastable configurations due to barriers for vortex entry. Data of the true
lower critical field H_c1 are presented. The low-temperature dependence of H_c1
is consistent with a superconducting state with nodes in the gap function.
[PACS numbers: 74.25.Bt, 74.60.Ec, 74.60.Ge, 74.72.Hs
Vortex Collisions: Crossing or Recombination?
We investigate the collision of two vortex lines moving with viscous dynamics
and driven towards each other by an applied current. Using London theory in the
approach phase we observe a non-trivial vortex conformation producing
anti-parallel segments; their attractive interaction triggers a violent
collision. The collision region is analyzed using the time-dependent
Ginzburg-Landau equation. While we find vortices will always recombine through
exchange of segments, a crossing channel appears naturally through a double
collision process.Comment: 4 pages, 3 figure
Quantum divisibility test and its application in mesoscopic physics
We present a quantum algorithm to transform the cardinality of a set of
charged particles flowing along a quantum wire into a binary number. The setup
performing this task (for at most N particles) involves log_2 N quantum bits
serving as counters and a sequential read out. Applications include a
divisibility check to experimentally test the size of a finite train of
particles in a quantum wire with a one-shot measurement and a scheme allowing
to entangle multi-particle wave functions and generating Bell states,
Greenberger-Horne-Zeilinger states, or Dicke states in a Mach-Zehnder
interferometer.Comment: 9 pages, 5 figure
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