37 research outputs found
On the lowest energy excitations of one-dimensional strongly correlated electrons
It is proven that the lowest excitations of one-dimensional
half-integer spin generalized Heisenberg models and half-filled extended
Hubbard models are -periodic functions. For Hubbard models at fractional
fillings , where , and is
the number of electrons per unit cell. Moreover, if one of the ground states of
the system is magnetic in the thermodynamic limit, then for
any , so the spectrum is gapless at any wave vector. The last statement is
true for any integer or half-integer value of the spin.Comment: 6 Pages, Revtex, final versio
Microstructural and morphological properties of homoepitaxial (001)ZnTe layers investigated by x-ray diffuse scattering
The microstructural and morphological properties of homoepitaxial (001)ZnTe
layers are investigated by x-ray diffuse scattering. High resolution reciprocal
space maps recorded close to the ZnTe (004) Bragg peak show different diffuse
scattering features. One kind of cross-shaped diffuse scattering streaks along
directions can be attributed to stacking faults within the epilayers.
Another kind of cross-shaped streaks inclined at an angle of about 80deg with
respect to the in-plane direction arises from the morphology of the
epilayers. (abridged version
Correlation between Crystallographic Alignment of Self-induced GaN Nanowires and Features of Si(111) Nitridation
Formation and spatial ordering of self-induced GaN nanowires grown by molecular beam epitaxy on a spatially pre-nitridazed Si(111) substrate have been studied. It was found the close correlation between Si substrate nitridation parameters and crystallographic alignment of NWs. Conditions for NWs nucleation and in- plane orientation are predefined by a structural anisotropy of silicon nitride nanolayer. Mechanism of NWs orderly emergence suggested.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3540
Incremental expansions for Hubbard-Peierls systems
The ground state energies of infinite half-filled Hubbard-Peierls chains are
investigated combining incremental expansion with exact diagonalization of
finite chain segments. The ground state energy of equidistant infinite Hubbard
(Heisenberg) chains is calculated with a relative error of less than for all values of using diagonalizations of 12-site (20-site)
chain segm ents. For dimerized chains the dimerization order parameter as a
function of the onsite repulsion interaction has a maximum at nonzero
values of , if the electron-phonon coupling is lower than a critical
value . The critical value is found with high accuracy to be
. For smaller values of the position of the maximum of is
approximately , and rapidly tends to zero as approaches from
below. We show how our method can be applied to calculate breathers for the
problem of phonon dynamics in Hubbard-Peierls systems.Comment: 4 Pages, 3 Figures, REVTE
The weak password problem: chaos, criticality, and encrypted p-CAPTCHAs
Vulnerabilities related to weak passwords are a pressing global economic and
security issue. We report a novel, simple, and effective approach to address
the weak password problem. Building upon chaotic dynamics, criticality at phase
transitions, CAPTCHA recognition, and computational round-off errors we design
an algorithm that strengthens security of passwords. The core idea of our
method is to split a long and secure password into two components. The first
component is memorized by the user. The second component is transformed into a
CAPTCHA image and then protected using evolution of a two-dimensional dynamical
system close to a phase transition, in such a way that standard brute-force
attacks become ineffective. We expect our approach to have wide applications
for authentication and encryption technologies.Comment: 5 pages, 6 figer
Universal Scaling of Wave Propagation Failure in Arrays of Coupled Nonlinear Cells
We study the onset of the propagation failure of wave fronts in systems of
coupled cells. We introduce a new method to analyze the scaling of the critical
external field at which fronts cease to propagate, as a function of
intercellular coupling. We find the universal scaling of the field throughout
the range of couplings, and show that the field becomes exponentially small for
large couplings. Our method is generic and applicable to a wide class of
cellular dynamics in chemical, biological, and engineering systems. We confirm
our results by direct numerical simulations.Comment: 4 pages, 3 figures, RevTe
On the correllation effect in Peierls-Hubbard chains
We reexamine the dimerization, the charge and the spin gaps of a half-filled
Peierls-Hubbard chain by means of the incremental expansion technique. Our
numerical findings are in significant quantitative conflict with recently
obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002)
697] based on a bosonization and a renormalization group method, especially
with respect to the charge gap. Their approach seems to be valid only in the
weakly correlated case.Comment: 7pages,4figures(6eps-files
Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine 8 PACS 85
Abstract. We consider the features of formation of AuTiPd ohmic contacts to p + -Si. Metallization was made by vacuum thermal sputtering of Pd, Ti and Au films onto the Si substrate heated up to 330 С. It is shown that the contact resistivity increases with temperature; this is typical of metallic conductivity. We suggest that the ohmic contact is formed owing to appearance of shunts at Pd deposition on dislocations or other structural defects. The number of shunts per unit area is close to the measured density of structural defects at the metalSi interface
Perturbation analysis of weakly discrete kinks
We present a perturbation theory of kink solutions of discrete Klein-Gordon
chains. The unperturbed solutions correspond to the kinks of the adjoint
partial differential equation. The perturbation theory is based on a
reformulation of the discrete chain problem into a partial differential
equation with spatially modulated mass density. The first order corrections to
the kink solutions are obtained analytically and are shown to agree with exact
numerical results. We discuss the problem of calculating the Peierls-Nabarro
barrier.Comment: 13 pages, 6 figures, REVTE
The polarizability model for ferroelectricity in perovskite oxides
This article reviews the polarizability model and its applications to
ferroelectric perovskite oxides. The motivation for the introduction of the
model is discussed and nonlinear oxygen ion polarizability effects and their
lattice dynamical implementation outlined. While a large part of this work is
dedicated to results obtained within the self-consistent-phonon approximation
(SPA), also nonlinear solutions of the model are handled which are of interest
to the physics of relaxor ferroelectrics, domain wall motions, incommensurate
phase transitions. The main emphasis is to compare the results of the model
with experimental data and to predict novel phenomena.Comment: 55 pages, 35 figure