1,178 research outputs found
Charge instabilities in strongly correlated bilayer systems
We investigate the charge-instabilities of the Hubbard-Holstein model with
two coupled layers. In this system the scattering processes naturally separate
into contributions which are either symmetric or antisymmetric combinations
with respect to exchange of the layers. It turns out that the short-range
strong correlations suppress finite wave-vector nesting instabilities for both
symmetries but favor the occurrence of phase separation in the symmetric
channel. Inclusion of a sizeable long-range Coulomb (LRC) interaction
frustrates the q=0 instabilities and supports the formation of incommensurate
charge-density waves (CDW). Upon reducing doping from half-filling and for
small electron-phonon coupling g the CDW instability first occurs in the
antisymmetric channel but both instability lines merge with increasing g. While
LRC forces always suppress the phase separation instability in the symmetric
channel, the CDW period in the antisymmetric sector tends to infinity (q_c ->
0) for sufficiently small Coulomb interaction. This feature allows for the
possibility of singular scattering over the whole Fermi surface. We discuss
possible implications of our results for the bilayer high-Tc cuprates.Comment: 14 pages, 8 figures, accepted for EPJ
Theory of isotope effect in photoemission spectra of high-T_c superconducting cuprates
We investigate the effect of isotope substitution on the electronic spectral
functions within a model where the charge carriers are coupled to bosonic
charge-order (CO) fluctuations centered around some mean frequency \omega_0 and
with enhanced scattering at wave-vector q_c. It is shown that a mass dependence
of \omega_0 is not sufficient in order to account, especially at high energies,
for the dispersion shifts experimentally observed in an optimally doped
superconducting cuprate. We argue that isotope substitution induces a change of
the spatial CO correlations which gives good account of the experimental data.Comment: 5 pages and 2 figure
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
Checkerboard and stripe inhomogeneities in cuprates
We systematically investigate charge-ordering phases by means of a restricted
and unrestricted Gutzwiller approximation to the single-band Hubbard model with
nearest () and next-nearest neighbor hopping (). When is small,
as appropriate for , stripes are found, whereas in
compounds with larger (such as and
) checkerboard structures are favored. In
contrast to the linear doping dependence found for stripes the charge
periodicity of checkerboard textures is locked to 4 unit cells over a wide
doping range. In addition we find that checkerboard structures are favored at
surfaces.Comment: 5 pages, 3 figure
Magnetic fluctuations from stripes in cuprates
Within the time-dependent Gutzwiller approximation for the Hubbard model we
compute the magnetic fluctuations of vertical metallic stripes with parameters
appropriate for LaBaCuO (LBCO). For bond- and
site-centered stripes the excitation spectra are similar, consisting of a
low-energy incommensurate acoustic branch which merges into a ``resonance
peak'' at the antiferromagnetic wave vector and several high-energy optical
branches. The acoustic branch is similar to the result of theories assuming
localized spins whereas the optical branches are significantly different.
Results are in good agreement with a recent inelastic neutron study of LBCO.Comment: 4 pages, 2 eps figure
Tax Compliance and Public Goods Provision -- An Agent-based Econophysics Approach
We calculate the dynamics of tax evasion within a multi-agent econophysics
model which is adopted from the theory of magnetism and previously has been
shown to capture the main characteristics from agent-based based models which
build on the standard Allingham and Sandmo approach. In particular, we
implement a feedback of public goods provision on the decision-making of
selfish agents which aim to pursue their self interest. Our results imply that
such a feedback enhances the moral attitude of selfish agents thus reducing the
percentage of tax evasion. Two parameters govern the behavior of selfish
agents, (i) the rate of adaption to changes in public goods provision and (ii)
the threshold of perception of public goods provision. Furtheron we analyze the
tax evasion dynamics for different agent co mpositions and under the feedback
of public goods provision. We conclude that policymakers may enhance tax
compliance behavior via the threshold of perception by means of targeted public
relations.Comment: 28 pages, 3 figures, accepted for publication in the Central European
Journal of Economic Modelling and Econometric
Odd parity charge density-wave scattering in cuprates
We investigate a model where superconducting electrons are coupled to a
frequency dependent charge-density wave (CDW) order parameter Delta(w). Our
approach can reconcile the simultaneous existence of low energy Bogoljubov
quasiparticles and high energy electronic order as observed in scanning
tunneling microscopy (STM) experiments. The theory accounts for the contrast
reversal in the STM spectra between positive and negative bias observed above
the pairing gap. An intrinsic relation between scattering rate and
inhomogeneities follows naturally.Comment: 5 pages, 3 figure
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