592 research outputs found
Hydrodynamics of liquids of arbitrarily curved flux-lines and vortex loops
We derive a hydrodynamic model for a liquid of arbitrarily curved flux-lines
and vortex loops using the mapping of the vortex liquid onto a liquid of
relativistic charged quantum bosons in 2+1 dimensions recently suggested by
Tesanovic and by Sudbo and collaborators. The loops in the flux-line system
correspond to particle-antiparticle fluctuations in the bosons. We explicitly
incorporate the externally applied magnetic field which in the boson model
corresponds to a chemical potential associated with the conserved charge
density of the bosons. We propose this model as a convenient and physically
appealing starting point for studying the properties of the vortex liquid
Continuous Melting of a "Partially Pinned" Two-Dimensional Vortex Lattice in a Square Array of Pinning Centers
The structure and equilibrium properties of a two-dimensional system of
superconducting vortices in a periodic pinning potential with square symmetry
are studied numerically. For a range of the strength of the pinning potential,
the low-temperature crystalline state exhibits only one of the two basic
periodicities (in the - and -directions) of the pinning potential. This
``partially pinned'' solid undergoes a continuous melting transition to a
weakly modulated liquid as the temperature is increased. A spin model,
constructed using symmetry arguments, is shown to reproduce the critical
behavior at this transition.Comment: 5 pages, 4 figure
Properties of the Bose glass phase in irradiated superconductors near the matching field
Structural and transport properties of interacting localized flux lines in
the Bose glass phase of irradiated superconductors are studied by means of
Monte Carlo simulations near the matching field B_Phi, where the densities of
vortices and columnar defects are equal. For a completely random columnar pin
distribution in the xy-plane transverse to the magnetic field, our results show
that the repulsive vortex interactions destroy the Mott insulator phase which
was predicted to occur at B = B_Phi. On the other hand, for ratios of the
penetration depth to average defect distance lambda/d <= 1, characteristic
remnants of the Mott insulator singularities remain visible in experimentally
accessible quantities as the magnetization, the bulk modulus, and the
magnetization relaxation, when B is varied near B_Phi. For spatially more
regular disorder, e.g., a nearly triangular defect distribution, we find that
the Mott insulator phase can survive up to considerably large interaction range
\lambda/d, and may thus be observable in experiments.Comment: RevTex, 17 pages, eps files for 12 figures include
Commensurate and Incommensurate Vortex Lattice Melting in Periodic Pinning Arrays
We examine the melting of commensurate and incommensurate vortex lattices
interacting with square pinning arrays through the use of numerical
simulations. For weak pinning strength in the commensurate case we observe an
order-order transition from a commensurate square vortex lattice to a
triangular floating solid phase as a function of temperature. This floating
solid phase melts into a liquid at still higher temperature. For strong pinning
there is only a single transition from the square pinned lattice to the liquid
state. For strong pinning in the incommensurate case, we observe a multi-stage
melting in which the interstitial vortices become mobile first, followed by the
melting of the entire lattice, consistent with recent imaging experiments. The
initial motion of vortices in the incommensurate phase occurs by an exchange
process of interstitial vortices with vortices located at the pinning sites. We
have also examined the vortex melting behavior for higher matching fields and
find that a coexistence of a commensurate pinned vortex lattice with an
interstitial vortex liquid occurs while at higher temperatures the entire
vortex lattice melts. For triangular arrays at incommensurate fields higher
than the first matching field we observe that the initial vortex motion can
occur through a novel correlated ring excitation where a number of vortices can
rotate around a pinned vortex. We also discuss the relevance of our results to
recent experiments of colloidal particles interacting with periodic trap
arrays.Comment: 8 figure
Galaxy rotation curves: the effect of j x B force
Using the Galaxy as an example, we study the effect of j x B force on the
rotational curves of gas and plasma in galaxies. Acceptable model for the
galactic magnetic field and plausible physical parameters are used to fit the
flat rotational curve for gas and plasma based on the observed baryonic
(visible) matter distribution and j x B force term in the static MHD equation
of motion. We also study the effects of varied strength of the magnetic field,
its pitch angle and length scale on the rotational curves. We show that j x B
force does not play an important role on the plasma dynamics in the
intermediate range of distances 6-12 kpc from the centre, whilst the effect is
sizable for larger r (r > 15 kpc), where it is the most crucial.Comment: Accepted for publication in Astrophysics & Space Science (final
printed version, typos in proofs corrected
Vortex states in 2D superconductor at high magnetic field in a periodic pinning potential
The effect of a periodic pinning array on the vortex state in a 2D
superconductor at low temperatures is studied within the framework of the
Ginzburg-Landau approach. It is shown that attractive interaction of vortex
cores to a commensurate pin lattice stabilizes vortex solid phases with long
range positional order against violent shear fluctuations. Exploiting a simple
analytical method, based on the Landau orbitals description, we derive a rather
detailed picture of the low temperatures vortex state phase diagram. It is
predicted that for sufficiently clean samples application of an artificial
periodic pinning array would enable one to directly detect the intrinsic shear
stiffness anisotropy characterizing the ideal vortex lattice.Comment: 8 pages, 5 figure
Peak effect and its evolution with defect structure in YBa2Cu3O7-d thin films at microwave frequencies
The vortex dynamics in YBa2Cu3O7-d thin films have been studied at microwave
frequencies. A pronounced peak in the surface resistance, Rs, is observed in
these films at frequencies of 4.88 and 9.55 GHz for magnetic fields varying
from 0.2 to 0.8 T. The peak is associated with an order-disorder transformation
of the flux line lattice as the temperature or field is increased. The
occurrence of the peak in Rs is crucially dependent on the depinning frequency,
wp and on the nature and concentration of growth defects present in these
films. Introduction of artificial defects by swift heavy ion irradiation with
200 MeV Ag ion at a fluence of 4x1010 ions/cm2 enhances wp and suppresses the
peak at 4.88 GHz but the peak at 9.55 GHz remains unaffected. A second peak at
lower temperature has also been observed at 9.55 GHz. This is related to twin
boundaries from angular dependence studies of Rs. Based on the temperature
variation of Rs, vortex phase diagrams have been constructed at 9.55 GHz.Comment: 8 pages, 4 figures Submitted to Physical Review
Time of arrival through interacting environments: Tunneling processes
We discuss the propagation of wave packets through interacting environments.
Such environments generally modify the dispersion relation or shape of the wave
function. To study such effects in detail, we define the distribution function
P_{X}(T), which describes the arrival time T of a packet at a detector located
at point X. We calculate P_{X}(T) for wave packets traveling through a
tunneling barrier and find that our results actually explain recent
experiments. We compare our results with Nelson's stochastic interpretation of
quantum mechanics and resolve a paradox previously apparent in Nelson's
viewpoint about the tunneling time.Comment: Latex 19 pages, 11 eps figures, title modified, comments and
references added, final versio
Formation of superdense hadronic matter in high energy heavy-ion collisions
We present the detail of a newly developed relativistic transport model (ART
1.0) for high energy heavy-ion collisions. Using this model, we first study the
general collision dynamics between heavy ions at the AGS energies. We then show
that in central collisions there exists a large volume of sufficiently
long-lived superdense hadronic matter whose local baryon and energy densities
exceed the critical densities for the hadronic matter to quark-gluon plasma
transition. The size and lifetime of this matter are found to depend strongly
on the equation of state. We also investigate the degree and time scale of
thermalization as well as the radial flow during the expansion of the
superdense hadronic matter. The flow velocity profile and the temperature of
the hadronic matter at freeze-out are extracted. The transverse momentum and
rapidity distributions of protons, pions and kaons calculated with and without
the mean field are compared with each other and also with the preliminary data
from the E866/E802 collaboration to search for experimental observables that
are sensitive to the equation of state. It is found that these inclusive,
single particle observables depend weakly on the equation of state. The
difference between results obtained with and without the nuclear mean field is
only about 20\%. The baryon transverse collective flow in the reaction plane is
also analyzed. It is shown that both the flow parameter and the strength of the
``bounce-off'' effect are very sensitive to the equation of state. In
particular, a soft equation of state with a compressibility of 200 MeV results
in an increase of the flow parameter by a factor of 2.5 compared to the cascade
case without the mean field. This large effect makes it possible to distinguish
the predictions from different theoretical models and to detect the signaturesComment: 55 pages, latex, + 39 figures available upon reques
Decoherence control in microwave cavities
We present a scheme able to protect the quantum states of a cavity mode
against the decohering effects of photon loss. The scheme preserves quantum
states with a definite parity, and improves previous proposals for decoherence
control in cavities. It is implemented by sending single atoms, one by one,
through the cavity. The atomic state gets first correlated to the photon number
parity. The wrong parity results in an atom in the upper state. The atom in
this state is then used to inject a photon in the mode via adiabatic transfer,
correcting the field parity. By solving numerically the exact master equation
of the system, we show that the protection of simple quantum states could be
experimentally demonstrated using presently available experimental apparatus.Comment: 13 pages, RevTeX, 8 figure
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