52 research outputs found
Growth Kinetics in a Phase Field Model with Continuous Symmetry
We discuss the static and kinetic properties of a Ginzburg-Landau spherically
symmetric model recently introduced (Phys. Rev. Lett. {\bf 75}, 2176,
(1995)) in order to generalize the so called Phase field model of Langer. The
Hamiltonian contains two invariant fields and bilinearly
coupled. The order parameter field evolves according to a non conserved
dynamics, whereas the diffusive field follows a conserved dynamics. In the
limit we obtain an exact solution, which displays an interesting
kinetic behavior characterized by three different growth regimes. In the early
regime the system displays normal scaling and the average domain size grows as
, in the intermediate regime one observes a finite wavevector
instability, which is related to the Mullins-Sekerka instability; finally, in
the late stage the structure function has a multiscaling behavior, while the
domain size grows as .Comment: 9 pages RevTeX, 9 figures included, files packed with uufiles to
appear on Phy. Rev.
A Soluble Phase Field Model
The kinetics of an initially undercooled solid-liquid melt is studied by
means of a generalized Phase Field model, which describes the dynamics of an
ordering non-conserved field phi (e.g. solid-liquid order parameter) coupled to
a conserved field (e.g. thermal field). After obtaining the rules governing the
evolution process, by means of analytical arguments, we present a discussion of
the asymptotic time-dependent solutions. The full solutions of the exact
self-consistent equations for the model are also obtained and compared with
computer simulation results. In addition, in order to check the validity of the
present model we confronted its predictions against those of the standard Phase
field model and found reasonable agreement. Interestingly, we find that the
system relaxes towards a mixed phase, depending on the average value of the
conserved field, i.e. on the initial condition. Such a phase is characterized
by large fluctuations of the phi field.Comment: 13 pages, 8 figures, RevTeX 3.1, submitted to Physical Review
Self-consistent scattering description of transport in normal-superconductor structures
We present a scattering description of transport in several
normal-superconductor structures. We show that the related requirements of
self-consistency and current conservation introduce qualitative changes in the
transport behavior when the current in the superconductor is not negligible.
The energy thresholds for quasiparticle propagation in the superconductor are
sensitive to the existence of condensate flow (). This dependence is
responsible for a rich variety of transport regimes, including a voltage range
in which only Andreev transmission is possible at the interfaces, and a state
of gapless superconductivity which may survive up to high voltages if
temperature is low. The two main effects of current conservation are a shift
towards lower voltages of the first peak in the differential conductance and an
enhancement of current caused by the greater availability of charge
transmitting scattering channels.Comment: 31 pages, 10 PS figures, Latex file, psfig.sty file is added. To
appear in Phys. Rev. B (Jan 97
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