1,514 research outputs found
Phase behavior of the Lattice Restricted Primitive Model with nearest-neighbor exclusion
The global phase behavior of the lattice restricted primitive model with
nearest neighbor exclusion has been studied by grand canonical Monte Carlo
simulations. The phase diagram is dominated by a fluid (or charge-disordered
solid) to charge-ordered solid transition that terminates at the maximum
density, and reduced temperature . At
that point, there is a first-order phase transition between two phases of the
same density, one charge-ordered and the other charge-disordered. The
liquid-vapor transition for the model is metastable, lying entirely within the
fluid-solid phase envelope.Comment: 6 pages, color. submitted to J. Chem. Phy
Phase diagrams in the lattice RPM model: from order-disorder to gas-liquid phase transition
The phase behavior of the lattice restricted primitive model (RPM) for ionic
systems with additional short-range nearest neighbor (nn) repulsive
interactions has been studied by grand canonical Monte Carlo simulations. We
obtain a rich phase behavior as the nn strength is varied. In particular, the
phase diagram is very similar to the continuum RPM model for high nn strength.
Specifically, we have found both gas-liquid phase separation, with associated
Ising critical point, and first-order liquid-solid transition. We discuss how
the line of continuous order-disorder transitions present for the low nn
strength changes into the continuum-space behavior as one increases the nn
strength and compare our findings with recent theoretical results by Ciach and
Stell [Phys. Rev. Lett. {\bf 91}, 060601 (2003)].Comment: 7 pages, 10 figure
Simplified solutions of the Cox-Thompson inverse scattering method at fixed energy
Simplified solutions of the Cox-Thompson inverse quantum scattering method at
fixed energy are derived if a finite number of partial waves with only even or
odd angular momenta contribute to the scattering process. Based on new formulae
various approximate methods are introduced which also prove applicable to the
generic scattering events.Comment: 9 pages, 3 figure
Numerical studies of the fractional quantum Hall effect in systems with tunable interactions
The discovery of the fractional quantum Hall effect in GaAs-based
semiconductor devices has lead to new advances in condensed matter physics, in
particular the possibility for exotic, topological phases of matter that
possess fractional, and even non-Abelian, statistics of quasiparticles. One of
the main limitations of the experimental systems based on GaAs has been the
lack of tunability of the effective interactions between two-dimensional
electrons, which made it difficult to stabilize some of the more fragile
states, or induce phase transitions in a controlled manner. Here we review the
recent studies that have explored the effects of tunability of the interactions
offered by alternative two-dimensional systems, characterized by non-trivial
Berry phases and including graphene, bilayer graphene and topological
insulators. The tunability in these systems is achieved via external fields
that change the mass gap, or by screening via dielectric plate in the vicinity
of the device. Our study points to a number of different ways to manipulate the
effective interactions, and engineer phase transitions between quantum Hall
liquids and compressible states in a controlled manner.Comment: 9 pages, 4 figures, updated references; review for the CCP2011
conference, to appear in "Journal of Physics: Conference Series
Diffusive transport in networks built of containers and tubes
We developed analytical and numerical methods to study a transport of
non-interacting particles in large networks consisting of M d-dimensional
containers C_1,...,C_M with radii R_i linked together by tubes of length l_{ij}
and radii a_{ij} where i,j=1,2,...,M. Tubes may join directly with each other
forming junctions. It is possible that some links are absent. Instead of
solving the diffusion equation for the full problem we formulated an approach
that is computationally more efficient. We derived a set of rate equations that
govern the time dependence of the number of particles in each container
N_1(t),N_2(t),...,N_M(t). In such a way the complicated transport problem is
reduced to a set of M first order integro-differential equations in time, which
can be solved efficiently by the algorithm presented here. The workings of the
method have been demonstrated on a couple of examples: networks involving
three, four and seven containers, and one network with a three-point junction.
Already simple networks with relatively few containers exhibit interesting
transport behavior. For example, we showed that it is possible to adjust the
geometry of the networks so that the particle concentration varies in time in a
wave-like manner. Such behavior deviates from simple exponential growth and
decay occurring in the two container system.Comment: 21 pages, 18 figures, REVTEX4; new figure added, reduced emphasis on
graph theory, additional discussion added (computational cost, one
dimensional tubes
Quantitative analysis of Sr2RuO4 ARPES spectra: Many-body interactions in a model Fermi liquid
ARPES spectra hold a wealth of information about the many-body interactions
in a correlated material. However, the quantitative analysis of ARPES spectra
to extract the various coupling parameters in a consistent manner is extremely
challenging, even for a model Fermi liquid system. We propose a fitting
procedure which allows quantitative access to the intrinsic lineshape,
deconvolved of energy and momentum resolution effects, of the correlated
2-dimensional material Sr2RuO4. For the first time in correlated 2-dimensional
materials, we find an ARPES linewidth that is narrower than its binding energy,
a key property of quasiparticles within Fermi liquid theory. We also find that
when the electron-electron scattering component is separated from the
electron-phonon and impurity scattering terms it decreases with a functional
form compatible with Fermi liquid theory as the Fermi energy is approached. In
combination with the previously determined Fermi surface, these results give
the first complete picture of a Fermi liquid system via ARPES. Furthermore, we
show that the magnitude of the extracted imaginary part of the self-energy is
in remarkable agreement with DC transport measurements.Comment: 10 pages, 5 figure
Formation of shock waves in a Bose-Einstein condensate
We consider propagation of density wave packets in a Bose-Einstein
condensate. We show that the shape of initially broad, laser-induced, density
perturbation changes in the course of free time evolution so that a shock wave
front finally forms. Our results are well beyond predictions of commonly used
zero-amplitude approach, so they can be useful in extraction of a speed of
sound from experimental data. We discuss a simple experimental setup for shock
propagation and point out possible limitations of the mean-field approach for
description of shock phenomena in a BEC.Comment: 8 pages & 6 figures, minor changes, more references, to appear in
Phys. Rev.
Heun Functions and the energy spectrum of a charged particle on a sphere under magnetic field and Coulomb force
We study the competitive action of magnetic field, Coulomb repulsion and
space curvature on the motion of a charged particle. The three types of
interaction are characterized by three basic lengths: l_{B} the magnetic
length, l_{0} the Bohr radius and R the radius of the sphere. The energy
spectrum of the particle is found by solving a Schr\"odinger equation of the
Heun type, using the technique of continued fractions. It displays a rich set
of functioning regimes where ratios \frac{R}{l_{B}} and \frac{R}{l_{0}} take
definite values.Comment: 12 pages, 5 figures, accepted to JOPA, november 200
Dynamics of Phase Transitions: The 3D 3-state Potts model
In studies of the QCD deconfining phase transition or cross-over by means of
heavy ion experiments, one ought to be concerned about non-equilibrium effects
due to heating and cooling of the system. In this paper we extend our previous
study of Glauber dynamics of 2D Potts models to the 3D 3-state Potts model,
which serves as an effective model for some QCD properties. We investigate the
linear theory of spinodal decomposition in some detail. It describes the early
time evolution of the 3D model under a quench from the disordered into the
ordered phase well, but fails in 2D. Further, the quench leads to competing
vacuum domains, which are difficult to equilibrate, even in the presence of a
small external magnetic field. From our hysteresis study we find, as before, a
dynamics dominated by spinodal decomposition. There is evidence that some
effects survive in the case of a cross-over. But the infinite volume
extrapolation is difficult to control, even with lattices as large as .Comment: 12 pages; added references, corrected typo
Simple and Robust Solver for the Poisson-Boltzmann Equation
A variational approach is used to develop a robust numerical procedure for
solving the nonlinear Poisson-Boltzmann equation. Following Maggs et al., we
construct an appropriate constrained free energy functional, such that its
Euler-Lagrange equations are equivalent to the Poisson-Boltzmann equation. We
then develop, implement, and test an algorithm for its numerical minimization,
which is quite simple and unconditionally stable. The analytic solution for
planar geometry is used for validation. Furthermore, some results are presented
for a charged colloidal sphere surrounded by counterions.Comment: 11 pages, 5 figures, 2 table
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