566 research outputs found
Pionic Degrees of Freedom in Atomic Nuclei and Quasielastic Knockout of Pions by High-Energy Electrons
The nonlinear model of pionic condensate in nuclei by G. Preparata can be
efficiently verified by investigation of the quasielastic knockout process of
pions out of nuclei by high energy electrons. First, a momentum distribution
(MD) of the collective pions has a bright maximum at q=0.3 Gev.Second the
excitation spectrum of a recoil nucleus is concentrated at low energies E
lesser than 1MeV. The results for the pion knockout from mesonic clouds of
individual nucleons are absolutely different. The latter results are presented
both for pion and rho-meson clouds localized on nucleons.Comment: 13 pages, 3 figure
Wavelength and intensity dependence of multiple forward scattering at above-threshold ionization in mid-infrared strong laser fields
The nonperturbative role of multiple forward scattering for Coulomb focusing
in mid-infrared laser fields and its dependence on a laser intensity and
wavelength are investigated for low-energy photoelectrons at above-threshold
ionization. We show that high-order rescattering events can have comparable
contributions to the Coulomb focusing and the effective number of rescattering
depends weakly on laser parameters in the classical regime. However, the
relative contribution of the forward scattering to the Coulomb focusing and the
Coulomb focusing in total decrease with the rise of the laser intensity and
wavelength
Optical Lattice Polarization Effects on Hyperpolarizability of Atomic Clock Transitions
The light-induced frequency shift due to the hyperpolarizability (i.e. terms
of second-order in intensity) is studied for a forbidden optical transition,
=0=0. A simple universal dependence on the field ellipticity is
obtained. This result allows minimization of the second-order light shift with
respect to the field polarization for optical lattices operating at a magic
wavelength (at which the first-order shift vanishes). We show the possibility
for the existence of a magic elliptical polarization, for which the
second-order frequency shift vanishes. The optimal polarization of the lattice
field can be either linear, circular or magic elliptical. The obtained results
could improve the accuracy of lattice-based atomic clocks.Comment: 4 pages, RevTeX4, 2 eps fig
Bichiral structure of feroelectric domain wall driven by flexoelectricity
The influence of flexoelectric coupling on the internal structure of neutral
domain walls in tetragonal phase of perovskite ferroelectrics is studied. The
effect is shown to lower the symmetry of 180-degree walls which are oblique
with respect to the cubic crystallographic axes, while {100} and {110} walls
stay "untouched". Being of the Ising type in the absence of the flexoelectric
interaction, the oblique domain walls acquire a new polarization component with
a structure qualitatively different from the classical Bloch-wall structure. In
contrast to the Bloch-type walls, where the polarization vector draws a helix
on passing from one domain to the other, in the flexoeffect-affected wall, the
polarization rotates in opposite directions on the two sides of the wall and
passes through zero in its center. Since the resulting polarization profile is
invariant upon inversion with respect to the wall center it does not brake the
wall symmetry in contrast to the classical Bloch-type walls. The flexoelectric
coupling lower the domain wall energy and gives rise to its additional
anisotropy that is comparable to that conditioned by the elastic anisotropy.
The atomic orderof- magnitude estimates shows that the new polarization
component P2 may be comparable with spontaneous polarization Ps, thus
suggesting that, in general, the flexoelectric coupling should be mandatory
included in domain wall simulations in ferroelectrics. Calculations performed
for barium titanate yields the maximal value of the P2, which is much smaller
than that of the spontaneous polarization. This smallness is attributed to an
anomalously small value of a component of the "strain-polarization"
elecrostictive tensor in this material
Correlation Between Structure And C-Afm Contrast Of 180-Degree Domain Walls In Rhombohedral Bati03
Using Landau-Ginzburg-Devonshire theory we describe 180-degree domain wall
structure, intrinsic energy and carrier accumulation in rhombohedral phase of
BaTiO3 as a function of the wall orientation and flexoelectric coupling
strength. Two types of domain wall structures (phases of the wall) exist
depending on the wall orientation. The low-energy 'achiral' phase occurs in the
vicinity of the {110} wall orientation and has odd polarization profile
invariant with respect to inversion about the wall center. The second 'chiral'
phase occurs around {211} wall orientations and corresponds to mixed parity
domain walls that may be of left-handed or right-handed chirality. The
transformation between the phases is abrupt, accompanied with 20-30% change of
the domain wall thickness and can happen at fixed wall orientation with
temperature change. We suggest that the phase transition may be detected
through domain wall thickness change or by c-AFM. The structure of the domain
wall is correlated to its conductivity through polarization component normal to
the domain wall, which causes free carriers accumulation. Depending on the
temperature and flexoelectric coupling strength relative conductivity of the
wall becomes at least one order of magnitude higher than in the single-domain
region, creating c-AFM contrast enhancement pronounced and detectable.Comment: 31 pages, 10 figures, Supplementary material
Polarization switching kinetics at the nanoscale in ferroelectric copolymer Langmuir-Blodgett films
The polarization switching kinetics of ferroelectric Langmuir–Blodgett films of vinylidene fluoride-trifluoroethylene copolymer were investigated by piezoresponse force microscopy with a resolution of 100 nm. The switching time in response to a localized voltage pulse exhibits an exponential dependence on reciprocal voltage, which is consistent with nucleation-limited switching dynamics
Tensor analyzing power Ayy in deuteron inclusive breakup at large Pt and spin structure of deuteron at short internucleonic distances
The Ayy data for deuteron inclusive breakup off hydrogen and carbon at a
deuteron momentum of 9.0 GeV/c and large Pt of emitted protons are presented.
The large values of Ayy independent of the target mass reflect the sensitivity
of the data to the deuteron spin structure. The data obtained at fixed and
plotted versus Pt clearly demonstrate the dependence of the deuteron spin
structure at short internucleonic distances on two variables. The data are
compared with the calculations using Paris, CD-Bonn and Karmanov's deuteron
wave functions.Comment: 4 pages, 2 figures, talk given at the SPIN2004 Conf., 10-16 Oct.
2004, Triest, Ital
Non-sequential double ionization below laser-intensity threshold: Anticorrelation of electrons without excitation of parent ion
Two-electron correlated spectra of non-sequential double ionization below
laser-intensity threshold are known to exhibit back-to-back scattering of the
electrons, viz., the anticorrelation of the electrons. Currently, the widely
accepted interpretation of the anticorrelation is recollision-induced
excitation of the ion plus subsequent field ionization of the second electron.
We argue that another mechanism, namely simultaneous electron emission, when
the time of return of the rescattered electron is equal to the time of
liberation of the bounded electron (the ion has no time for excitation), can
also explain the anticorrelation of the electrons in the deep below
laser-intensity threshold regime. Our conclusion is based on the results of the
numerical solution of the time-dependent Schr\"{o}dinger equation for a model
system of two one-dimensional electrons as well as an adiabatic analytic model
that allows for a closed-form solution.Comment: 6 pages and 3 figure
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