6,387 research outputs found
Critical behavior of Josephson-junction arrays at f=1/2
The critical behavior of frustrated Josephson-junction arrays at flux
quantum per plaquette is considered. Results from Monte Carlo simulations and
transfer matrix computations support the identification of the critical
behavior of the square and triangular classical arrays and the one-dimensional
quantum ladder with the universality class of the XY-Ising model. In the
quantum ladder, the transition can happen either as a simultaneous ordering of
the and order parameters or in two separate stages, depending on
the ratio between interchain and intrachain Josephson couplings. For the
classical arrays, weak random plaquette disorder acts like a random field and
positional disorder as random bonds on the variables. Increasing
positional disorder decouples the and variables leading to the
same critical behavior as for integer .Comment: 9 pages, Latex, workshop on JJA, to appear in Physica
Phase-coherence transition in granular superconductors with junctions
We study the three-dimensional XY-spin glass as a model for the resistive
behavior of granular superconductors containing a random distribution of
junctions, as in high- superconducting materials with d-wave symmetry. The
junctions leads to quenched in circulating currents (chiralities) and to
a chiral-glass state at low temperatures, even in the absence of an external
magnetic field. Dynamical simulations in the phase representation are used to
determine the nonlinear current-voltage characteristics as a function of
temperature. Based on dynamic scaling analysis, we find a phase-coherence
transition at finite temperature below which the linear resistivity should
vanish and determine the corresponding critical exponents. The results suggest
that the phase and chiralities may order simultaneously for decreasing
temperatures into a superconducting chiral-glass state.Comment: 5 pages, 1 figure, Proc. of ICM 2000, to appear in J. Magn. Magn.
Mate
Phase transitions in the one-dimensional frustrated quantum XY model and Josephson-junction ladders
A one-dimensional quantum version of the frustrated XY (planar rotor) model
is considered which can be physically realized as a ladder of
Josephson-junctions at half a flux quantum per plaquette. This system undergoes
a superconductor to insulator transition at zero temperature as a function of
charging energy. The critical behavior is studied using a Monte Carlo transfer
matrix applied to the path-integral representation of the model and a
finite-size-scaling analysis of data on small system sizes. Depending on the
ratio between the interchain and intrachain couplings the system can have
single or double transitions which is consistent with the prediction that its
critical behavior should be described by the two-dimensional classical XY-Ising
model.Comment: 13 pages, Revtex, J. Appl. Phys. (to appear), Inpe-las-00
Phase and vortex correlations in Josephson-junction arrays at irrational frustration
Phase coherence and vortex order in a Josephson-junction array at irrational
frustration are studied by extensive Monte Carlo simulations using the parallel
tempering method. A scaling analysis of the correlation length of phase
variables in the full equilibrated system shows that the critical temperature
vanishes with a power-law divergent correlation length and critical exponent
, in agreement with recent results from resistivity scaling analysis.
A similar scaling analysis for vortex variables reveals a different critical
exponent , suggesting that there are two distinct correlation lengths
associated with a decoupled zero-temperature phase transition.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
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