39,999 research outputs found
Screening in Ionic Systems: Simulations for the Lebowitz Length
Simulations of the Lebowitz length, , are reported
for t he restricted primitive model hard-core (diameter ) 1:1 electrolyte
for densi ties and .
Finite-size eff ects are elucidated for the charge fluctuations in various
subdomains that serve to evaluate . On extrapolation to the
bulk limit for the low-density expansions (Bekiranov and
Fisher, 1998) are seen to fail badly when (with ). At highe r densities rises above the Debye
length, \xi_{\text{D}} \prop to \sqrt{T/\rho}, by 10-30% (upto ); the variation is portrayed fairly well by generalized
Debye-H\"{u}ckel theory (Lee and Fisher, 19 96). On approaching criticality at
fixed or fixed , remains finite with
but displays a
weak entropy-like singularity.Comment: 4 pages 5 figure
Vortex Fluctuations in the Critical Casimir Effect of Superfluid and Superconducting Films
Vortex-loop renormalization techniques are used to calculate the magnitude of
the critical Casimir forces in superfluid films. The force is found to become
appreciable when size of the thermal vortex loops is comparable to the film
thickness, and the results for T < Tc are found to match very well with
perturbative renormalization theories that have only been carried out for T >
Tc. When applied to a high-Tc superconducting film connected to a bulk sample,
the Casimir force causes a voltage difference to appear between the film and
bulk, and estimates show that this may be readily measurable.Comment: 4 pages, 5 figures, Revtex 4, typo correctio
Asymmetric Fluid Criticality I: Scaling with Pressure Mixing
The thermodynamic behavior of a fluid near a vapor-liquid and, hence,
asymmetric critical point is discussed within a general ``complete'' scaling
theory incorporating pressure mixing in the nonlinear scaling fields as well as
corrections to scaling. This theory allows for a Yang-Yang anomaly in which
\mu_{\sigma}^{\prime\prime}(T), the second temperature derivative of the
chemical potential along the phase boundary, diverges like the specific heat
when T\to T_{\scriptsize c}; it also generates a leading singular term,
|t|^{2\beta}, in the coexistence curve diameter, where t\equiv
(T-T_{\scriptsize c}) /T_{\scriptsize c}. The behavior of various special loci,
such as the critical isochore, the critical isotherm, the k-inflection loci, on
which \chi^{(k)}\equiv \chi(\rho,T)/\rho^{k} (with \chi = \rho^{2}
k_{\scriptsize B}TK_{T}) and C_{V}^{(k)}\equiv C_{V}(\rho,T)/\rho^{k} are
maximal at fixed T, is carefully elucidated. These results are useful for
analyzing simulations and experiments, since particular, nonuniversal values of
k specify loci that approach the critical density most rapidly and reflect the
pressure-mixing coefficient. Concrete illustrations are presented for the
hard-core square-well fluid and for the restricted primitive model electrolyte.
For comparison, a discussion of the classical (or Landau) theory is presented
briefly and various interesting loci are determined explicitly and illustrated
quantitatively for a van der Waals fluid.Comment: 21 pages in two-column format including 8 figure
Discretization Dependence of Criticality in Model Fluids: a Hard-core Electrolyte
Grand canonical simulations at various levels, -20, of fine- lattice
discretization are reported for the near-critical 1:1 hard-core electrolyte or
RPM. With the aid of finite-size scaling analyses it is shown convincingly
that, contrary to recent suggestions, the universal critical behavior is
independent of (\grtsim 4); thus the continuum RPM
exhibits Ising-type (as against classical, SAW, XY, etc.) criticality. A
general consideration of lattice discretization provides effective
extrapolation of the {\em intrinsically} erratic -dependence, yielding
(\Tc^ {\ast},\rhoc^{\ast})\simeq (0.0493_{3},0.075) for the
RPM.Comment: 4 pages including 4 figure
Complete high-precision entropic sampling
Monte Carlo simulations using entropic sampling to estimate the number of
configurations of a given energy are a valuable alternative to traditional
methods. We introduce {\it tomographic} entropic sampling, a scheme which uses
multiple studies, starting from different regions of configuration space, to
yield precise estimates of the number of configurations over the {\it full
range} of energies, {\it without} dividing the latter into subsets or windows.
Applied to the Ising model on the square lattice, the method yields the
critical temperature to an accuracy of about 0.01%, and critical exponents to
1% or better. Predictions for systems sizes L=10 - 160, for the temperature of
the specific heat maximum, and of the specific heat at the critical
temperature, are in very close agreement with exact results. For the Ising
model on the simple cubic lattice the critical temperature is given to within
0.003% of the best available estimate; the exponent ratios and
are given to within about 0.4% and 1%, respectively, of the
literature values. In both two and three dimensions, results for the {\it
antiferromagnetic} critical point are fully consistent with those of the
ferromagnetic transition. Application to the lattice gas with nearest-neighbor
exclusion on the square lattice again yields the critical chemical potential
and exponent ratios and to good precision.Comment: For a version with figures go to
http://www.fisica.ufmg.br/~dickman/transfers/preprints/entsamp2.pd
Stability of Elastic Glass Phases in Random Field XY Magnets and Vortex Lattices in Type II Superconductors
A description of a dislocation-free elastic glass phase in terms of domain
walls is developed and used as the basis of a renormalization group analysis of
the energetics of dislocation loops added to the system. It is found that even
after optimizing over possible paths of large dislocation loops, their energy
is still very likely to be positive when the dislocation core energy is large.
This implies the existence of an equilibrium elastic glass phase in three
dimensional random field X-Y magnets, and a dislocation free,
bond-orientationally ordered ``Bragg glass'' phase of vortices in dirty Type II
superconductors.Comment: 12 pages, Revtex, no figures, submitted to Phys Rev Letter
The Roton Fermi Liquid
We introduce and analyze a novel metallic phase of two-dimensional (2d)
electrons, the Roton Fermi Liquid (RFL), which, in contrast to the Landau Fermi
liquid, supports both gapless fermionic and bosonic quasiparticle excitations.
The RFL is accessed using a re-formulation of 2d electrons consisting of
fermionic quasiparticles and vortices interacting with a mutual
long-ranged statistical interaction. In the presence of a strong
vortex-antivortex (i.e. roton) hopping term, the RFL phase emerges as an exotic
yet eminently tractable new quantum ground state. The RFL phase exhibits a
``Bose surface'' of gapless roton excitations describing transverse current
fluctuations, has off-diagonal quasi-long-ranged order (ODQLRO) at zero
temperature (T=0), but is not superconducting, having zero superfluid density
and no Meissner effect. The electrical resistance {\it vanishes} as
with a power of temperature (and frequency), (with ), independent of the impurity concentration. The RFL phase also has a full
Fermi surface of quasiparticle excitations just as in a Landau Fermi liquid.
Electrons can, however, scatter anomalously from rotonic "current
fluctuations'' and "superconducting fluctuations'', leading to "hot" and "cold"
spots. Fermionic quasiparticles dominate the Hall electrical transport. We also
discuss instabilities of the RFL to a conventional Fermi liquid and a
superconductor. Precisely {\it at} the instability into the Fermi liquid state,
the exponent , so that . Upon entering the
superconducting state the anomalous quasiparticle scattering is strongly
suppressed. We discuss how the RFL phenomenology might apply to the cuprates.Comment: 43 page
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