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

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

Extended Hubbard model in the presence of a magnetic field

Within the Green's function and equations of motion formalism it is possible to exactly solve a large class of models useful for the study of strongly correlated systems. Here, we present the exact solution of the one-dimensional extended Hubbard model with on-site $U$ and first nearest neighbor repulsive V interactions in the presence of an external magnetic field h, in the narrow band limit. At zero temperature our results establish the existence of four phases in the three-dimensional space (U, n, h) - n is the filling - with relative phase transitions, as well as different types of charge ordering. The magnetic field may dramatically affect the behavior of thermodynamic quantities, inducing, for instance, magnetization plateaus in the magnetization curves, and a change from a single to a double-peak structure in the specific heat. According to the value of the particle density, we find one or two critical fields, marking the beginning of full or partial polarization. A detailed study of several thermodynamic quantities is also presented at finite temperature.Comment: 11 pages, 12 figures. EPJB Topical Issue on Novel Quantum Phases and Mesoscopic Physics in Quantum Gase

Magnetic and thermal properties of a one-dimensional spin-1 model

We study the one-dimensional S=1 Blume-Emery-Griffiths model. Upon transforming the spin model into an equivalent fermionic model, we provide the exact solution within the Green's function and equations of motion formalism. We show that the relevant response functions as well as thermodynamic quantities can be determined, in the whole parameters space, in terms of a finite set of local correlators. Furthermore, considering the case of an antiferromagnetic chain with single-ion anisotropy in the presence of an external magnetic field, we find three plateaus in the magnetization curve; in the neighborhood of the endpoints of the intermediate plateau, the specific heat shows a double peak structure.Comment: 7 pages, 4 figures. This paper is dedicated to Professor Igor Stasyuk on the occasion of his 70th birthda

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

Visual distortion of body size modulates pain perception

Pain is a complex subjective experience, that can be shaped by several cognitive, psychological and even contextual variables. For example, simply viewing the body reduces the reported intensity of acute physical pain. We investigated whether this visually induced analgesia can be modulated by the visually depicted size of the stimulated body part. We measured contact heat-pain thresholds, while participants viewed either their own hand or a neutral object, at real size, enlarged, or reduced. Vision of the body was analgesic, increasing heat-pain thresholds by ~ 4°C. Importantly, enlargement of the viewed hand enhanced this analgesia, while looking at a reduced hand decreased it. These results demonstrate that visual distortions of body size modulate sensory components of pain, and reveal a clear functional relation between the perception of pain and the representation of the body