11,660 research outputs found
Different orderings in the narrow-band limit of the extended Hubbard model on the Bethe lattice
We present the exact solution of a system of Fermi particles living on the
sites of a Bethe lattice with coordination number z and interacting through
on-site U and nearest-neighbor V interactions. This is a physical realization
of the extended Hubbard model in the atomic limit. Within the Green's function
and equations of motion formalism, we provide a comprehensive analysis of the
model and we study the phase diagram at finite temperature in the whole model's
parameter space, allowing for the on-site and nearest-neighbor interactions to
be either repulsive or attractive. We find the existence of critical regions
where charge ordering (V>0) and phase separation (V<0) are observed. This
scenario is endorsed by the study of several thermodynamic quantities.Comment: 17 pages, 20 figure
One-dimensional extended Hubbard model in the atomic limit
We present the exact solution of the one-dimensional extended Hubbard model
in the atomic limit within the Green's function and equation of motion
formalism. We provide a comprehensive and systematic analysis of the model by
considering all the relevant response and correlation functions as well as
thermodynamic quantities in the whole parameter space. At zero temperature we
identify four phases in the plane (U,n) [U is the onsite potential and n is the
filling] and relative phase transitions as well as different types of charge
ordering. These features are endorsed by investigating at T=0 the chemical
potential and pertinent local correlators, the particle and double occupancy
correlation functions, the entropy, and by studying the behavior in the limit T
going to zero of the charge and spin susceptibilities. A detailed study of the
thermodynamic quantities is also presented at finite temperature. This study
evidences that a finite-range order persists for a wide range of the
temperature, as shown by the behavior of the correlation functions and by the
two-peak structure exhibited by the charge susceptibility and by the entropy.
Moreover, the equation of motion formalism, together with the use of composite
operators, allows us to exactly determine the set of elementary excitations. As
a result, the density of states can be determined exactly and a detailed
analysis of the specific heat allows for identifying the excitations and for
ascribing its two-peak structure to a redistribution of the charge density.Comment: 28 pages;added references and corrected typos. This paper is an
extended version of Phys. Rev. E 77, 061120 (2008
Magnetic behavior of a spin-1 Blume-Emery-Griffiths model
I study the one-dimensional spin-1 Blume-Emery-Griffiths model with bilinear
and biquadratic exchange interactions and single-ion crystal field under an
applied magnetic field. This model can be exactly mapped into a tight-binding
Hubbard model - extended to include intersite interactions - provided one
renormalizes the chemical and the on-site potentials, which become temperature
dependent. After this transformation, I provide the exact solution of the
Blume-Emery-Griffiths model in one dimension by means of the Green's functions
and equations of motion formalism. I investigate the magnetic variations of
physical quantities - such as magnetization, quadrupolar moment, susceptibility
- for different values of the interaction parameters and of the applied field,
focusing on the role played by the biquadratic interaction in the breakdown of
the magnetization plateaus.Comment: 4 pages, 5 figures. ICM 2009 (Karlsruhe) Conference proceeding
Role of the attractive intersite interaction in the extended Hubbard model
We consider the extended Hubbard model in the atomic limit on a Bethe lattice
with coordination number z. By using the equations of motion formalism, the
model is exactly solved for both attractive and repulsive intersite potential
V. By focusing on the case of negative V, i.e., attractive intersite
interaction, we study the phase diagram at finite temperature and find, for
various values of the filling and of the on-site coupling U, a phase transition
towards a state with phase separation. We determine the critical temperature as
a function of the relevant parameters, U/|V|, n and z and we find a reentrant
behavior in the plane (U/|V|,T). Finally, several thermodynamic properties are
investigated near criticality.Comment: 7 pages, 7 figures. EPJB Topical Issue on Novel Quantum Phases and
Mesoscopic Physics in Quantum Gase
Integration of the VIMOS control system
The VIRMOS consortium of French and Italian Institutes (PI: O. Le Fevre,
co-PI: G. Vettolani) is manufacturing two wide field imaging multi-object
spectrographs for the European Southern Observatory Very Large Telescope (VLT),
with emphasis on the ability to carry over spectroscopic surveys of large
numbers of sources: the VIsible Multi-Object Spectrograph, VIMOS, and the Near
InfraRed Multi-Object Spectrograph, NIRMOS. There are 52 motors to be
controlled in parallel in the spectrograph, making VIMOS a complex machine to
be handled. This paper will focus on the description of the control system,
designed in the ESO VLT standard control concepts, and on some integration
issues and problem solving strategies.Comment: 3 pages, 3 figures, ICALEPCS 2001 Conference, PSN#TUBT00
Engineering an interaction and entanglement between distant atoms
We propose a scheme to generate an effective interaction of arbitrary
strength between the internal degrees of freedom of two atoms placed in distant
cavities connected by an optical fiber. The strength depends on the field
intensity in the cavities. As an application of this interaction, we calculate
the amount of entanglement it generates between the internal states of the
distant atoms. The scheme effectively converts entanglement distribution
networks to networks of interacting spins.Comment: published versio
Self-Consistent Mean-Field Theory for Frustrated Josephson Junction Arrays
We review the self-consistent mean-field theory for charge-frustrated
Josephson junction arrays. Using (\phi is the phase of the
superconducting wavefunction) as order parameter and imposing the
self-consistency condition, we compute the phase boundary line between the
superconducting region ( not equal to zero) and the insulating one
( = 0). For a uniform offset charge q=e the superconducting phase
increases with respect to the situation in which q=0. Here, we generalize the
self-consistent mean-field theory to include the effects induced by a random
distribution of offset charges and/or of diagonal self-capacitances. For most
of the phase diagram, our results agree with the outcomes of Quantum Monte
Carlo simulations as well as with previous studies using the path-integral
approach.Comment: Presented by F. P. Mancini at the Conference "Highlights in Condensed
Matter Physics", May 9-11 2003, Salerno, Ital
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