4,655 research outputs found
Magnetic Raman scattering of the ordered tetrahedral spin-1/2 clusters in Cu_2Te_2O_5(Br_(1-x)Cl_x)_2 compounds
Raman light-scattering experiments in the antiferromagnetic phase of the
Cu_2Te_2O_5(Br_(1-x)Cl_x)_2 compounds are analyzed in terms of a dimerized spin
model for the tetrahedral Cu-clusters. It is shown that the longitudinal
magnetic excitation in the pure Br system hybridizes with a localized singlet
excitation due to the presence of a Dzyaloshinskii-Moriya anisotropy term. The
drastic change of the magnetic scattering intensities observed when a
proportion of Br is replaced by Cl ions, is proposed to be caused by a change
of the magnetic order parameter. Instead of being parallel/antiparallel with
each other, the spins in the two pairs of spin-1/2 order perpendicular to each
other, when the composition x is larger than about 0.25.Comment: EPL, in pres
Vertex routing models
A class of models describing the flow of information within networks via
routing processes is proposed and investigated, concentrating on the effects of
memory traces on the global properties. The long-term flow of information is
governed by cyclic attractors, allowing to define a measure for the information
centrality of a vertex given by the number of attractors passing through this
vertex. We find the number of vertices having a non-zero information centrality
to be extensive/sub-extensive for models with/without a memory trace in the
thermodynamic limit. We evaluate the distribution of the number of cycles, of
the cycle length and of the maximal basins of attraction, finding a complete
scaling collapse in the thermodynamic limit for the latter. Possible
implications of our results on the information flow in social networks are
discussed.Comment: 12 pages, 6 figure
Внутриглазная гипертензия у больных передними эндогенными увеитами: факторы риска развития и лечение
Проведено ретроспективний аналіз 195 історій хвороб пацієнтів з передніми ендогенними увеїтами, які знаходилися на лікуванні в Кримському республіканському центрі мікрохірургії ока у період з січня 2004 по листопад 2009. Кількість очей з підвищенням внутрішньоочного тиску (ВОТ) була 24,6 %. Підвищення ВОТ у хворих хронічними увеїтами виникало в 3 рази частіше, ніж у хворих гострими увеїтами (p < 0,05). Визначена позитивна кореляція між віком пацієнтів, тривалістю місцевого краплинного вживання кортикостероїдів і підвищенням ВОТ (r = 0,7). У більшості хворих (93 %) компенсація ВОТ була досягнута медикаментозно.The retrospective analysis of 195 case reports of patients with endogenous anterior uveitis, which were in the Crimean republican ophthalmologic microsurgical center in a period from January 2004 to November 2009, was performed. The prevalence of raised intraocular pressure (IOP) in the study eyes was 24,6 %. The odds ratio for raised IOP in chronic uveitis as compared with acute uveitis was 3 (p < 0,05). Steroid usage and increasing age were significantly correlated with raised IOP (r = 0,7). The majority of these eyes (93 %) were treated medically
Quasiparticle spectral weights of Gutzwiller-projected high T_c superconductors
We analyze the electronic Green's functions in the superconducting ground
state of the t-J model using Gutzwiller-projected wave functions, and compare
them to the conventional BCS form. Some of the properties of the BCS state are
preserved by the projection: the total spectral weight is continuous around the
quasiparticle node and approximately constant along the Fermi surface. On the
other hand, the overall spectral weight is reduced by the projection with a
momentum-dependent renormalization, and the projection produces electron-hole
asymmetry in renormalization of the electron and hole spectral weights. The
latter asymmetry leads to the bending of the effective Fermi surface which we
define as the locus of equal electron and hole spectral weight.Comment: 6 pages, 5 figures; x-labels on Figs. 1 and 2 corrected, footnote on
particle number corrected, references adde
Tunnelling matrix elements with antiferromagnetic Gutzwiller wave functions
We use a generalized Gutzwiller Approximation (GA) elaborated to evaluate
matrix elements with partially projected wave functions and formerly applied to
homogeneous systems.
In the present paper we consider projected single-particle (hole) excitations
for electronic systems with antiferromagnetic (AFM) order and obtain the
corresponding tunnelling probabilities. The accuracy and the reliability of our
analytical approximation is tested using the Variational Monte Carlo (VMC).
Possible comparisons with experimental results are also discussed.Comment: 16 pages, 10 figure
A Variational Monte Carlo Study of the Current Carried by a Quasiparticle
With the use of Gutzwiller-projected variational states, we study the
renormalization of the current carried by the quasiparticles in
high-temperature superconductors and of the quasiparticle spectral weight. The
renormalization coefficients are computed by the variational Monte Carlo
technique, under the assumption that quasiparticle excitations may be described
by Gutzwiller-projected BCS quasiparticles. We find that the current
renormalization coefficient decreases with decreasing doping and tends to zero
at zero doping. The quasiparticle spectral weight Z_+ for adding an electron
shows an interesting structure in k space, which corresponds to a depression of
the occupation number k just outside the Fermi surface. The perturbative
corrections to those quantities in the Hubbard model are also discussed.Comment: 9 pages, 9 figure
Electronic structure of strongly correlated d-wave superconductors
We study the electronic structure of a strongly correlated d-wave
superconducting state. Combining a renormalized mean field theory with direct
calculation of matrix elements, we obtain explicit analytical results for the
nodal Fermi velocity, v_F, the Fermi wave vector, k_F, and the momentum
distribution, n_k, as a function of hole doping in a Gutzwiller projected
d-wave superconductor. We calculate the energy dispersion, E_k, and spectral
weight of the Gutzwiller-Bogoliubov quasiparticles, and find that the spectral
weight associated with the quasiparticle excitation at the antinodal point
shows a non monotonic behavior as a function of doping. Results are compared to
angle resolved photoemission spectroscopy (ARPES) of the high temperature
superconductors.Comment: final version, comparison to experiments added, 4+ pages, 4 figure
Pseudogap and antiferromagnetic correlations in the Hubbard model
Using the dynamical cluster approximation and quantum monte carlo we
calculate the single-particle spectra of the Hubbard model with next-nearest
neighbor hopping . In the underdoped region, we find that the pseudogap
along the zone diagonal in the electron doped systems is due to long range
antiferromagnetic correlations. The physics in the proximity of is
dramatically influenced by and determined by the short range correlations.
The effect of on the low energy ARPES spectra is weak except close to the
zone edge. The short range correlations are sufficient to yield a pseudogap
signal in the magnetic susceptibility, produce a concomitant gap in the
single-particle spectra near but not necessarily at a location in
the proximity of Fermi surface.Comment: 5 pages, 4 figure
Pairing and superconductivity driven by strong quasiparticle renormalization in two-dimensional organic charge transfer salts
We introduce and analyze a variational wave function for quasi
two-dimensional kappa-ET organic salts containing strong local and nonlocal
correlation effects. We find an unconventional superconducting ground state for
intermediate charge carrier interaction, sandwiched between a conventional
metal at weak coupling and a spin liquid at larger coupling. Most remarkably,
the excitation spectrum is dramatically renormalized and is found to be the
driving force for the formation of the unusual superconducting state.Comment: 4 pages, 4 figure
Synthesis and Properties of Dipyridylcyclopentenes
A short and general route to the substituted dipyridylcyclopentenes was explored and several new compounds belonging to this new group of diarylethenes were synthesized. The study of their photochromic and thermochromic properties shows that the rate of the thermal ring opening is strongly dependent on the polarity of the solvent.
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