514 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
Spontaneous Magnetization of the O(3) Ferromagnet at Low Temperatures
We investigate the low-temperature behavior of ferromagnets with a
spontaneously broken symmetry O(3) O(2). The analysis is performed within
the perspective of nonrelativistic effective Lagrangians, where the dynamics of
the system is formulated in terms of Goldstone bosons. Unlike in a
Lorentz-invariant framework (chiral perturbation theory), where loop graphs are
suppressed by two powers of momentum, loops involving ferromagnetic spin waves
are suppressed by three momentum powers. The leading coefficients of the
low-temperature expansion for the partition function are calculated up to order
. In agreement with Dyson's pioneering microscopic analysis of the
cubic ferromagnet, we find that, in the spontaneous magnetization, the
magnon-magnon interaction starts manifesting itself only at order . The
striking difference with respect to the low-temperature properties of the O(3)
antiferromagnet is discussed from a unified point of view, relying on the
effective Lagrangian technique.Comment: 23 pages, 4 figure
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
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
Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?
Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are
explained by an elaborately modified spin-wave theory. We give a strong
evidence of the major contribution to 1/T_1_ being made by the three-magnon
scattering rather than the Raman one.Comment: J. Phys.: Condens. Matter 16, No. 49, 9023 (2004
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
Differential cross sections for muonic atom scattering in solid hydrogenic targets
The differential cross sections for low-energy muonic hydrogen atom
scattering in solid molecular H, D and T targets under low pressure
have been calculated for various temperatures. The polycrystalline fcc and hcp
structure of the solid hydrogenic targets are considered. The Bragg and phonon
scattering processes are described using the Debye model of a solid. The
calculated cross sections are used for Monte Carlo simulations of the muonic
atom slowing down in these targets. They have been successfully applied for a
description of the production of the muonic atom beams in the multilayer
hydrogenic crystals.Comment: 23 pages, 19 figures, 2 table
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