477 research outputs found
Local electronic nematicity in the one-band Hubbard model
Nematicity is a well known property of liquid crystals and has been recently
discussed in the context of strongly interacting electrons. An electronic
nematic phase has been seen by many experiments in certain strongly correlated
materials, in particular, in the pseudogap phase generic to many hole-doped
cuprate superconductors. Recent measurements in high superconductors has
shown even if the lattice is perfectly rotationally symmetric, the ground state
can still have strongly nematic local properties. Our study of the
two-dimensional Hubbard model provides strong support of the recent
experimental results on local rotational symmetry breaking. The
variational cluster approach is used here to show the possibility of an
electronic nematic state and the proximity of the underlying symmetry-breaking
ground state within the Hubbard model. We identify this nematic phase in the
overdoped region and show that the local nematicity decreases with increasing
electron filling. Our results also indicate that strong Coulomb interaction may
drive the nematic phase into a phase similar to the stripe structure. The
calculated spin (magnetic) correlation function in momentum space shows the
effects resulting from real-space nematicity
Le nombre d’Avogadro en prend pour son rhume : l’homéopathie en question
Même si de plus en plus de psychoéducateurs utilisent
des approches appuyées sur des données probantes, ils
sont également confrontés dans leur pratique quotidienne
à des approches dites alternatives dont la validité, dans
la majorité des cas, reste à démontrer. Parmi celles-ci,
l’homéopathie prétend traiter un ensemble de problèmes psychosociaux dont le TDAH, les troubles d’apprentissage, l’anxiété, la peur, etc. L’objectif
de cet article est de considérer la pertinence de cette approche non seulement pour traiter les
problèmes psychosociaux mais également l’ensemble des troubles qu’elle prétend soigner.
Cet article comprend cinq parties. Dans la première, nous situons l’histoire de l’homéopathie
dans le cadre de la chimie et de la pharmacologie modernes. La deuxième est consacrée
à ce qu’il est convenu maintenant d’appeler « l’affaire de la mémoire de l’eau » que des
homéopathes ont tenté de récupérer à leur profit pour justifier l’activité de leurs produits
même lorsque la dilution de ceux-ci est telle qu’ils ne contiennent plus de molécule active.
Au cours de la troisième partie, nous faisons état de la recherche concernant l’efficacité
des traitements homéopathiques. Dans la quatrième partie, nous montrons brièvement que
l’homéopathie vétérinaire n’est pas plus efficace que l’homéopathie appliquée aux humains.
Dans la cinquième partie, nous soulevons quelques aspects éthiques en soulignant entre
autres éléments que la prescription des produits homéopathiques et l’utilisation des
« vaccins » de même nature ne sont pas sans conséquences.Although there is an increasing body of psychoeducators who rely on evidence-based
approaches, it is also common for them to employ alternative methods in the context of their
daily practice. More often than not, the validity of these theories has yet to be established.
Among the complementary approaches, homeopathy is one that could supposedly treat
various psychosocial problems, including ADHD, learning disorders, anxiety, fear, etc. The
objective of this article is to determine whether or not such an alternative therapy should be
considered an appropriate course of treatment for psychosocial issues as well as all of the
other disorders allegedly treated by homeopathy. This article is divided into five parts. Firstly,
we discuss the historical background of homeopathy in the context of modern chemistry
and pharmacology. The second part of this text is dedicated to what is nowadays referred
to as ‘’water memory’’, a concept seized by homeopaths in an attempt to justify their claims
regarding the efficiency of products lacking active molecules due to over-dilution. Thirdly,
we outline the current state of research concerning the effectiveness of homeopathic
treatments. In part four, we briefly demonstrate that veterinary homeopathy isn’t more
efficient than homeopathy applied to humans. Finally, in part five, we ponder the ethical
issues surrounding the prescription of homeopathic products and the use of vaccines of the
same nature in consideration of their potential consequences
Interest as Damages
In this article, we posit that when arbitral tribunals decide international disputes, they typically fail to fully compensate claimants for the loss of the use of their money. This failure occurs because they do not acknowledge that businesses typically invest in opportunities that pose a significantly greater risk than the risk reflected in such commonly used standards as U.S. T-bills and LIBOR rates. Claimants also must share the blame when they do not set out a well-constructed claim for interest as damages. However, even when claimants do so, tribunals often award damages at a statutory rate or at rate reflecting a nearly risk-free investment because they are unfamiliar with modern economic and financial principles. We propose changing this practice. We set out a legal framework for allowing an award of interest as damages and then furnish a model for claimants and tribunals to use. Under this model, interest accrues at a risk-free interest rate plus a market risk premium with the interest award to be compounded on a yearly basis. This model would bring awards in line with modern economic realities and more accurately compensate injured parties
Characteristics of oxygen isotope substitutions in the quasiparticle spectrum of BiSrCaCuO
There is an ongoing debate about the nature of the bosonic excitations
responsible for the quasiparticle self energy in high temperature
superconductors -- are they phonons or spin fluctuations? We present a careful
analysis of the bosonic excitations as revealed by the `kink' feature at 70 meV
in angle resolved photoemission data using Eliashberg theory for a d-wave
superconductor. Starting from the assumption that nodal quasiparticles are not
coupled to the magnetic resonance, the sharp structure at meV
can be assigned to phonons. We find that not only can we account for the shifts
of the kink energy seen on oxygen isotope substitution but also get a
quantitative estimate of the fraction of the area under the electron-boson
spectral density which is due to phonons. We conclude that for optimally doped
BiSrCaCuO phonons contribute % and
non-phononic excitations %.Comment: 6 pages, 3 figure
Cluster Perturbation Theory for Hubbard models
Cluster perturbation theory is a technique for calculating the spectral
weight of Hubbard models of strongly correlated electrons, which combines exact
diagonalizations on small clusters with strong-coupling perturbation theory at
leading order. It is exact in both the strong- and weak-coupling limits and
provides a good approximation to the spectral function at any wavevector.
Following the paper by S\'en\'echal et al. (Phys. Rev. Lett. {\bf 84}, 522
(2000)), we provide a more complete description and derivation of the method.
We illustrate some of its capabilities, in particular regarding the effect of
doping, the calculation of ground state energy and double occupancy, the
disappearance of the Fermi surface in the Hubbard model, and so on. The
method is applicable to any model with on-site repulsion only.Comment: 11 pages, 10 figures (RevTeX 4
Spectral functions for strongly correlated 5f-electrons
We calculate the spectral functions of model systems describing 5f-compounds
adopting Cluster Perturbation Theory. The method allows for an accurate
treatment of the short-range correlations. The calculated excitation spectra
exhibit coherent 5f bands coexisting with features associated with local
intra-atomic transitions. The findings provide a microscopic basis for partial
localization. Results are presented for linear chains.Comment: 10 Page
Semiclassical description of spin ladders
The Heisenberg spin ladder is studied in the semiclassical limit, via a
mapping to the nonlinear model. Different treatments are needed if the
inter-chain coupling is small, intermediate or large. For intermediate
coupling a single nonlinear model is used for the ladder. Its predicts
a spin gap for all nonzero values of if the sum of the spins
of the two chains is an integer, and no gap otherwise. For small , a better
treatment proceeds by coupling two nonlinear sigma models, one for each chain.
For integer , the saddle-point approximation predicts a sharp drop
in the gap as increases from zero. A Monte-Carlo simulation of a spin 1
ladder is presented which supports the analytical results.Comment: 8 pages, RevTeX 3.0, 4 PostScript figure
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