24,296 research outputs found
Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders
Using the Density Matrix Renormalization Group and two-leg ladders, we
investigate an electronic two-orbital Hubbard model including plaquette
diagonal hopping amplitudes. Our goal is to search for regimes where charges
added to the undoped state form pairs, presumably a precursor of a
superconducting state.For the electronic density , i.e. the undoped
limit, our investigations show a robust antiferromagnetic ground
state, as in previous investigations. Doping away from and for large
values of the Hund coupling , a ferromagnetic region is found to be stable.
Moreover, when the interorbital on-site Hubbard repulsion is smaller than the
Hund coupling, i.e. for in the standard notation of multiorbital Hubbard
models, our results indicate the coexistence of pairing tendencies and
ferromagnetism close to . These results are compatible with previous
investigations using one dimensional systems. Although further research is
needed to clarify if the range of couplings used here is of relevance for real
materials, such as superconducting heavy fermions or pnictides, our theoretical
results address a possible mechanism for pairing that may be active in the
presence of short-range ferromagnetic fluctuations.Comment: 8 pages, 4 Fig
An episode mimicking a versive seizure in acute bilateral pontine stroke.
Pontine ischemia usually results in focal deficits such as hemiparesis, facial palsy, dysarthria, disorders of eye movements or vertigo. Although rarely described, involuntary abnormal movements and "convulsions" due to pontine lesions can also occur. Here we describe a 67-year-old woman with hypertension who presented with a tonic movement mimicking a versive seizure in the acute phase of bilateral pontine ischemia. Post-stroke movement disorders are well known. They are usually associated with supratentorial lesions and rarely occur in the acute phase, but "seizure-like" episodes can be seen in pontine ischemia. Awareness of this rare phenomenon is useful for the management of acute stroke patients
Non-Hermitian robust edge states in one-dimension: Anomalous localization and eigenspace condensation at exceptional points
Capital to topological insulators, the bulk-boundary correspondence ties a
topological invariant computed from the bulk (extended) states with those at
the boundary, which are hence robust to disorder. Here we put forward an
ordering unique to non-Hermitian lattices, whereby a pristine system becomes
devoid of extended states, a property which turns out to be robust to disorder.
This is enabled by a peculiar type of non-Hermitian degeneracy where a
macroscopic fraction of the states coalesce at a single point with geometrical
multiplicity of , that we call a phenomenal point.Comment: 6 pages, 4 figure
Nucleon-to-Delta axial transition form factors in relativistic baryon chiral perturbation theory
We report a theoretical study of the axial Nucleon to Delta(1232)
() transition form factors up to one-loop order in relativistic
baryon chiral perturbation theory. We adopt a formalism in which the
couplings obey the spin-3/2 gauge symmetry and, therefore, decouple the
unphysical spin-1/2 fields. We compare the results with phenomenological form
factors obtained from neutrino bubble chamber data and in quark models.Comment: A few clarifying remarks added; version to appear in Physical Review
Multi-site H-bridge breathers in a DNA--shaped double strand
We investigate the formation process of nonlinear vibrational modes
representing broad H-bridge multi--site breathers in a DNA--shaped double
strand.
Within a network model of the double helix we take individual motions of the
bases within the base pair plane into account. The resulting H-bridge
deformations may be asymmetric with respect to the helix axis. Furthermore the
covalent bonds may be deformed distinctly in the two backbone strands.
Unlike other authors that add different extra terms we limit the interaction
to the hydrogen bonds within each base pair and the covalent bonds along each
strand. In this way we intend to make apparent the effect of the characteristic
helicoidal structure of DNA. We study the energy exchange processes related
with the relaxation dynamics from a non-equilibrium conformation. It is
demonstrated that the twist-opening relaxation dynamics of a radially distorted
double helix attains an equilibrium regime characterized by a multi-site
H-bridge breather.Comment: 27 pages and 10 figure
Gauge Field Theory in the Infrared Regime
We propose that the low energy behavior of a pure gauge theory can be studied
by simply assuming violation of Lorentz invariance which is implemented through
a deformation of the canonical Poisson brackets of the theory depending on an
infrared scale. The resulting theory is equivalent to a pure gauge theory with
a Chern-Simons like term. It is shown that at low energies this theory can be
identified with three dimensional QCD where the mass of the fermion is related
to the infrared scale.Comment: 4pp, ReVte
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