143,598 research outputs found
Enhanced Screening in Chemically Functionalized Graphene
Resonant scatterers such as hydrogen adatoms can strongly enhance the low
energy density of states in graphene. Here, we study the impact of these
impurities on the electronic screening. We find a two-faced behavior: Kubo
formula calculations reveal an increased dielectric function upon
creation of midgap states but no metallic divergence of the static
at small momentum transfer . This bad metal behavior
manifests also in the dynamic polarization function and can be directly
measured by means of electron energy loss spectroscopy. A new length scale
beyond which screening is suppressed emerges, which we identify with the
Anderson localization length.Comment: 5 pages, 4 figure
Dual-fermion approach to the Anderson-Hubbard model
We apply the recently developed dual fermion algorithm for disordered
interacting systems to the Anderson-Hubbard model. This algorithm is compared
with dynamical cluster approximation calculations for a one-dimensional system
to establish the quality of the approximation in comparison with an established
cluster method. We continue with a three-dimensional (3d) system and look at
the antiferromagnetic, Mott and Anderson localization transitions. The dual
fermion approach leads to quantitative as well as qualitative improvement of
the dynamical mean-field results and it allows one to calculate the hysteresis
in the double occupancy in 3d taking into account nonlocal correlations
Localization of strongly correlated electrons as Jahn-Teller polarons in manganites
A realistic modeling of manganites should include the Coulomb repulsion
between electrons, the Hund's rule coupling to spins, and
Jahn-Teller phonons. Solving such a model by dynamical mean field theory, we
report large magnetoresistances and spectra in good agreement with experiments.
The physics of the unusual, insulating-like paramagnetic phase is determined by
correlated electrons which are-due to strong correlations-easily trapped as
Jahn-Teller polarons.Comment: 4 pages, 3 figure
Customer anger and incentives for quality provision
Emotions are a significant determinant of consumer behaviour. A customer may get angry if he feels that he is being treated unfairly by his supplier and that anger may make him more likely to switch to an alternative provider. We model the strategic interaction between firms that choose quality levels and anger-prone customers who pick their supplier based on their expectations of suppliers' quality. Strategic interaction can allow for multiple equilibria including some in which no firm invests in high quality. Allowing customers to voice their anger on peer-review fora can eliminate low-quality equilibria, and may even support a unique equilibrium in which all firms choose high quality
Orbital selective crossover and Mott transitions in an asymmetric Hubbard model of cold atoms in optical lattices
We study the asymmetric Hubbard model at half-filling as a generic model to
describe the physics of two species of repulsively interacting fermionic cold
atoms in optical lattices. We use Dynamical Mean Field Theory to obtain the
paramagnetic phase diagram of the model as function of temperature, interaction
strength and hopping asymmetry. A Mott transition with a region of two
coexistent solutions is found for all nonzero values of the hopping asymmetry.
At low temperatures the metallic phase is a heavy Fermi-liquid, qualitatively
analogous to the Fermi liquid state of the symmetric Hubbard model. Above a
coherence temperature, an orbital-selective crossover takes place, wherein one
fermionic species effectively localizes, and the resulting bad metallic state
resembles the non-Fermi liquid state of the Falicov-Kimball model. We compute
observables relevant to cold atom systems such as the double occupation, the
specific heat and entropy and characterize their behavior in the different
phases
Quantum phase transition in the two-band Hubbard model
The interaction between itinerant and Mott localized electronic states in
strongly correlated materials is studied within dynamical mean field theory in
combination with the numerical renormalization group method. A novel
nonmagnetic zero temperature quantum phase transition is found in the
bad-metallic orbital-selective Mott phase of the two-band Hubbard model, for
values of the Hund's exchange which are relevant to typical transition metal
oxides.Comment: 4 pages, 4 eps figures, revised version, to appear in Phys. Rev. Let
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