36 research outputs found
Fano-like anti-resonances in strongly coupled binary Coulomb systems
Molecular Dynamics (MD) simulations of a strongly coupled binary ionic
mixture have revealed the appearance of sharp minima in the species resolved
dynamical density fluctuation spectra. This phenomenon is reminiscent of the
well-known Fano anti-resonance, occurring in various physical processes. We
give a theoretical analysis using the Quasi Localized Charge Approximation, and
demonstrate that the observed phenomenon in the equilibrium spectrum is a novel
manifestation of the Fano mechanism, that occurs at characteristic frequencies
of the system different from the conventional classical Fano frequencies
Ground state structures of superparamagnetic 2D dusty plasma crystals
Ground state structures of finite, cylindrically confined two-dimensional
Yukawa systems composed of charged superparamagnetic dust grains in an external
magnetic field are investigated numerically, using molecular dynamic
simulations and lattice summation methods. The ground state configuration of
the system is identified using, as an approximation, the experimentally
obtained shape of the horizontal confinement potential in a classical single
layer dusty plasma experiment with non-magnetic grains. Results are presented
for the dependence of the number density and lattice parameters of the dust
layer on (1) the ratio of the magnetic dipole-dipole force to electrostatic
force between the grains and (2) the orientation of the grain magnetic moment
with respect to the layer.Comment: submitted to Phys. Rev.
Dielectric matrix and plasmon dispersion in strongly coupled electronic bilayer liquids
We develop a dielectric matrix and analyze plasmon dispersion in strongly
coupled charged-particle bilayers in the quantum domain. The formulation is
based on the classical quasi-localized charge approximation (QLCA) and extends
the QLCA formalism into the quantum domain. Its development, which parallels
that of 2D companion paper [Phys. Rev. E 70, 026406 (2004)] by three of the
authors, generalizes the single-layer scalar formalism therein to a bilayer
matrix formalism. Using pair correlation function data generated from diffusion
Monte Carlo simulations, we calculate the dispersion of the in-phase and
out-of-phase plasmon modes over a wide range of in-layer coupling values and
layer spacings. The out-of-phase spectrum exhibits an exchange-correlation
induced long-wavelength energy gap in contrast to earlier predictions of
acoustic dispersion softened by exchange-correlations. The energy gap is
similar to what has been previously predicted for classical charged-particle
bilayers and subsequently confirmed by recent molecular dynamics computer
simulations.Comment: 53 pages including 15 Figures with their captions. Submitted to
Physical Review
Factorization of 3-point static structure functions in 3D Yukawa liquids
In many-body systems the convolution approximation states that the 3-point
static structure function, , can
approximately be "factorized" in terms of the 2-point counterpart,
. We investigate the validity of this approximation in
3-dimensional strongly-coupled Yukawa liquids: the factorization is tested for
specific arrangements of the wave vectors and
, with molecular dynamics simulations. With the increase of the
coupling parameter we find a breakdown of factorization, of which a notable
example is the appearance of negative values of
, whereas the approximate factorized
form is restricted to positive values. These negative values -- based on the
quadratic Fluctuation-Dissipation Theorem -- imply that the quadratic part of
the density response of the system changes sign with wave number. Our
simulations that incorporate an external potential energy perturbation clearly
confirm this behavior
Is the Vlasov equation valid for Yukawa plasmas?
We analyze the Vlasov dispersion relation for Yukawa plasmas in three
dimensions for the purpose of identifying coupling parameter domains where the
Vlasov approach is justified and the existence of a well-developed RPA type
collective excitation is allowed. We establish a rigorous lower bound for the
coupling parameter, below which there can be no real solution to the Vlasov
dispersion relation. In the coupling domain, where weakly damped solutions do
exist, we have focused on the long-wavelength acoustic regime where we
establish more restrictive estimates for the lower bound of the coupling
parameter. We also derive a general formula for the corresponding acoustic
phase velocity, valid over a wide range of coupling parameter/screening
parameter ratios above the lower bound. We conclude that the Vlasov approach is
tenable only above a critical coupling value. Comparison with Molecular
Dynamics simulation results further highlights the limitations of the Vlasov
approximation for weakly coupled Yukawa plasmas
Linear and quadratic static response functions and structure functions in Yukawa liquids
We compute linear and quadratic static density response functions of three-dimensional Yukawa liquids by applying an external perturbation potential in molecular dynamics simulations. The response functions are also obtained from the equilibrium fluctuations (static structure factors) in the system via the fluctuation-dissipation theorems. The good agreement of the quadratic response functions, obtained in the two different ways, confirms the quadratic fluctuation-dissipation theorem. We also find that the three-point structure function may be factorizable into two-point structure functions, leading to a cluster representation of the equilibrium triplet correlation function