3,242 research outputs found
Stripe formation in electron-doped cuprates
We investigate the formation of charge domain walls in an electron-doped
extended Hubbard model for the superconducting cuprates. Within an unrestricted
Hartree-Fock approach, extended by the introduction of slave-bosons to obtain a
more proper treatment of strong correlations, we demonstrate the occurrence of
stripes in the (1,1) and (1,-1) directions having one doped electron per stripe
site. The different filling, direction and width of these electron-doped
stripes with respect to those obtained in the hole-doped systems have
interesting observable consequences, which are discussed.Comment: 4 pages, 2 encapsulated postscript figure
Charge inhomogeneity coexisting with large Fermi surfaces
We discuss how stripes in cuprates can be compatible with a Fermi-liquid-like
Fermi surface and, at the same time, they give rise to a one-dimensional-like
pseudo Fermi surface in the momentum distribution function.Comment: Proceedings of the M2S conference, July 2006, Dresden; 2 pages, 1
figure to appear on Phisica
Fermi surface dichotomy on systems with fluctuating order
We investigate the effect of a dynamical collective mode coupled with
quasiparticles at specific wavevectors only. This coupling describes the
incipient tendency to order and produces shadow spectral features at high
energies, while leaving essentially untouched the low energy quasiparticles.
This allows to interpret seemingly contradictory experiments on underdoped
cuprates, where many converging evidences indicate the presence of charge
(stripe or checkerboard) order, which remains instead elusive in the Fermi
surface obtained from angle-resolved photoemission experiments.Comment: 11 pages, 10 figure
Cooperation, competition and the emergence of criticality in communities of adaptive systems
The hypothesis that living systems can benefit from operating at the vicinity
of critical points has gained momentum in recent years. Criticality may confer
an optimal balance between exceedingly ordered and too noisy states. We here
present a model, based on information theory and statistical mechanics,
illustrating how and why a community of agents aimed at understanding and
communicating with each other converges to a globally coherent state in which
all individuals are close to an internal critical state, i.e. at the borderline
between order and disorder. We study --both analytically and computationally--
the circumstances under which criticality is the best possible outcome of the
dynamical process, confirming the convergence to critical points under very
generic conditions. Finally, we analyze the effect of cooperation (agents try
to enhance not only their fitness, but also that of other individuals) and
competition (agents try to improve their own fitness and to diminish those of
competitors) within our setting. The conclusion is that, while competition
fosters criticality, cooperation hinders it and can lead to more ordered or
more disordered consensual solutions.Comment: 20 pages, 5 figures. Supplementary Material: 8 page
The Electron-Phonon Interaction in the Presence of Strong Correlations
We investigate the effect of strong electron-electron repulsion on the
electron-phonon interaction from a Fermi-liquid point of view: the strong
interaction is responsible for vertex corrections, which are strongly dependent
on the ratio. These corrections generically lead to a strong
suppression of the effective coupling between quasiparticles mediated by a
single phonon exchange in the limit. However, such effect
is not present when . Analyzing the Landau stability
criterion, we show that a sizable electron-phonon interaction can push the
system towards a phase-separation instability. A detailed analysis is then
carried out using a slave-boson approach for the infinite-U three-band Hubbard
model. In the presence of a coupling between the local hole density and a
dispersionless optical phonon, we explicitly confirm the strong dependence of
the hole-phonon coupling on the transferred momentum versus frequency ratio. We
also find that the exchange of phonons leads to an unstable phase with negative
compressibility already at small values of the bare hole-phonon coupling. Close
to the unstable region, we detect Cooper instabilities both in s- and d-wave
channels supporting a possible connection between phase separation and
superconductivity in strongly correlated systems.Comment: LateX 3.14, 04.11.1994 Preprint no.101
Adult dorsal root ganglia sensory neurons express the early neuronal fate marker doublecortin
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