245 research outputs found
The S(0) structure in highly compressed hydrogen and the orientational transition
A calculation of the rotational S(0) frequencies in high pressure solid
para-hydrogen is performed. Convergence of the perturbative series at high
density is demonstrated by the calculation of second and third order terms. The
results of the theory are compared with the available experimental data to
derive the density behaviour of structural parameters. In particular, a strong
increase of the value of the lattice constant ratio and of the
internuclear distance is determined. Also a decrease of the anisotropic
intermolecular potential is observed which is attributed to charge transfer
effects. The structural parameters determined at the phase transition may be
used to calculate quantum properties of the rotationally ordered phase.Comment: accepted Europhysics Letter
Weighted-density approximation for general nonuniform fluid mixtures
In order to construct a general density-functional theory for nonuniform
fluid mixtures, we propose an extension to multicomponent systems of the
weighted-density approximation (WDA) of Curtin and Ashcroft [Phys. Rev. A 32,
2909 (1985)]. This extension corrects a deficiency in a similar extension
proposed earlier by Denton and Ashcroft [Phys. Rev. A 42, 7312 (1990)], in that
that functional cannot be applied to the multi-component nonuniform fluid
systems with spatially varying composition, such as solid-fluid interfaces. As
a test of the accuracy of our new functional, we apply it to the calculation of
the freezing phase diagram of a binary hard-sphere fluid, and compare the
results to simulation and the Denton-Ashcroft extension.Comment: 4 pages, 4 figures, to appear in Phys. Rev. E as Brief Repor
Nanostratification of optical excitation in self-interacting 1D arrays
The major assumption of the Lorentz-Lorenz theory about uniformity of local
fields and atomic polarization in dense material does not hold in finite groups
of atoms, as we reported earlier [A. E. Kaplan and S. N. Volkov, Phys. Rev.
Lett., v. 101, 133902 (2008)]. The uniformity is broken at sub-wavelength
scale, where the system may exhibit strong stratification of local field and
dipole polarization, with the strata period being much shorter than the
incident wavelength. In this paper, we further develop and advance that theory
for the most fundamental case of one-dimensional arrays, and study nanoscale
excitation of so called "locsitons" and their standing waves (strata) that
result in size-related resonances and related large field enhancement in finite
arrays of atoms. The locsitons may have a whole spectrum of spatial
frequencies, ranging from long waves, to an extent reminiscent of ferromagnetic
domains, -- to super-short waves, with neighboring atoms alternating their
polarizations, which are reminiscent of antiferromagnetic spin patterns. Of
great interest is the new kind of "hybrid" modes of excitation, greatly
departing from any magnetic analogies. We also study differences between
Ising-like near-neighbor approximation and the case where each atom interacts
with all other atoms in the array. We find an infinite number of "exponential
eigenmodes" in the lossless system in the latter case. At certain "magic"
numbers of atoms in the array, the system may exhibit self-induced (but linear
in the field) cancellation of resonant local-field suppression. We also studied
nonlinear modes of locsitons and found optical bistability and hysteresis in an
infinite array for the simplest modes.Comment: 39 pages, 5 figures; v2: Added the Conclusions section, corrected a
typo in Eq. (5.3), corrected minor stylistic and grammatical imperfection
Equilibrium phase behavior of polydisperse hard spheres
We calculate the phase behavior of hard spheres with size polydispersity,
using accurate free energy expressions for the fluid and solid phases. Cloud
and shadow curves, which determine the onset of phase coexistence, are found
exactly by the moment free energy method, but we also compute the complete
phase diagram, taking full account of fractionation effects. In contrast to
earlier, simplified treatments we find no point of equal concentration between
fluid and solid or re-entrant melting at higher densities. Rather, the fluid
cloud curve continues to the largest polydispersity that we study (14%); from
the equilibrium phase behavior a terminal polydispersity can thus only be
defined for the solid, where we find it to be around 7%. At sufficiently large
polydispersity, fractionation into several solid phases can occur, consistent
with previous approximate calculations; we find in addition that coexistence of
several solids with a fluid phase is also possible
Ювілей Михайла Миколайовича Тарана
18 жовтня 2008 р. виповнилося 60 років відомому українському вченому-мінералогу, знаному в світі фахівцю в галузі фізики мінералів, доктору геолого-мінералогічних наук Михайлові Миколайовичу Тарану
Modelling colloids with Baxter's adhesive hard sphere model
The structure of the Baxter adhesive hard sphere fluid is examined using
computer simulation. The radial distribution function (which exhibits unusual
discontinuities due to the particle adhesion) and static structure factor are
calculated with high accuracy over a range of conditions and compared with the
predictions of Percus--Yevick theory. We comment on rigidity in percolating
clusters and discuss the role of the model in the context of experiments on
colloidal systems with short-range attractive forces.Comment: 14 pages, 7 figures. (For proceedings of "Structural arrest in
colloidal systems with short-range attractive forces", Messina, December
2003
Quantum and Classical Orientational Ordering in Solid Hydrogen
We present a unified view of orientational ordering in phases I, II, and III
of solid hydrogen. Phases II and III are orientationally ordered, while the
ordering objects in phase II are angular momenta of rotating molecules, and in
phase III the molecules themselves. This concept provides quantitative
explanation of the vibron softening, libron and roton spectra, and increase of
the IR vibron oscillator strength in phase III. The temperature dependence of
the effective charge parallels the frequency shifts of the IR and Raman
vibrons. All three quantities are linear in the order parameter.Comment: Replaced with the final text, accepted for publication in PRL. 1 Fig.
added. Misc. text revision
First-Principle Homogenization Theory for Periodic Metamaterials
We derive from first principles an accurate homogenized description of
periodic metamaterials made of magnetodielectric inclusions, highlighting and
overcoming relevant limitations of standard homogenization methods. We obtain
closed-form expressions for the effective constitutive parameters, pointing out
the relevance of inherent spatial dispersion effects, present even in the
long-wavelength limit. Our results clarify the limitations of quasi-static
homogenization models, restore the physical meaning of homogenized metamaterial
parameters and outline the reasons behind magnetoelectric coupling effects that
may arise also in the case of center-symmetric inclusions.Comment: 58 pages, 10 figures Phys. Rev. B, in press (2011
High Magnetic Field NMR Studies of LiVGeO, a quasi 1-D Spin System
We report Li pulsed NMR measurements in polycrystalline and single
crystal samples of the quasi one-dimensional S=1 antiferromagnet
LiVGeO, whose AF transition temperature is K.
The field () and temperature () ranges covered were 9-44.5 T and
1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice
relaxation rate (), and the spin-phase relaxation rate (),
often as a function of the orientation of the field relative to the crystal
axes. The spectra indicate an AF magnetic structure consistent with that
obtained from neutron diffraction measurements, but with the moments aligned
parallel to the c-axis. The spectra also provide the -dependence of the AF
order parameter and show that the transition is either second order or weakly
first order. Both the spectra and the data show that has at
most a small effect on the alignment of the AF moment. There is no spin-flop
transition up to 44.5 T. These features indicate a very large magnetic
anisotropy energy in LiVGeO with orbital degrees of freedom playing an
important role. Below 8 K, varies substantially with the orientation
of in the plane perpendicular to the c-axis, suggesting a small energy
gap for magnetic fluctuations that is very anisotropic.Comment: submitted to Phys. Rev.
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