Role of the attractive intersite interaction in the extended Hubbard model (original) (raw)
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Exact solution of the extended Hubbard model in the atomic limit on the Bethe Lattice
2007
We study the phase diagram at finite temperature of a system of Fermi particles on the sites of the Bethe lattice with coordination number z and interacting through onsite U and nearest-neighbor V interactions. This is a physical realization of the extended Hubbard model in the atomic limit. By using the equations of motion method, we exactly solve the model. For an attractive intersite potential, we find, at half filling, a phase transition towards a broken particle-hole symmetry state. The critical temperature, as a function of the relevant parameters, has a re-entrant behavior as already observed in the equivalent spin-1 Ising model on the Bethe lattice.
Acta Physica Polonica A, 2012
We have studied a simple effective model of charge ordered insulators. The tight binding Hamiltonian consists of the effective on-site interaction U and the intersite density-density interaction Wij (both: nearest-neighbor and next-nearest-neighbor). In the analysis of the phase diagrams and thermodynamic properties of this model we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. Our investigations of the general case (as a function of the electron concentration n) have shown that the system exhibits various critical behaviors including among others bicritical, tricritical, critical-end and isolated critical points. In this report we concentrate on the metastable phases and transitions between them. One finds that the first-and second order transitions between metastable phases can exist in the system. These transitions occur in the neighborhood of first as well as second order transitions between stable phases. For the case of on-site attraction the regions of metastable homogeneous phases occurrence inside the ranges of phase separated states stability have been also determined.
Journal of Physics: Condensed Matter, 2011
We have studied the extended Hubbard model in the atomic limit. The Hamiltonian analyzed consists of the effective on-site interaction U and the intersite density-density interactions Wij (both: nearest-neighbour and next-nearest-neighbour). The model can be considered as a simple effective model of charge ordered insulators. The phase diagrams and thermodynamic properties of this system have been determined within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. Our investigation of the general case taking into account for the first time the effects of longer-ranged density-density interaction (repulsive and attractive) as well as possible phase separations shows that, depending on the values of the interaction parameters and the electron concentration, the system can exhibit not only several homogeneous charge ordered (CO) phases, but also various phase separated states (CO-CO and CO-nonordered). One finds that the model considered exhibits very interesting multicritical behaviours and features, including among others bicritical, tricritical, critical-end and isolated critical points.
Acta Physica Polonica A, 2015
We analyze the extended Hubbard model with pairhopping interaction J, i.e. the PensonKolbHubbard model, in the case of repulsive J (J < 0) within the (broken symmetry) HartreeFock approximation. We focus our study on the eects of on-site U interaction on the mutual stability of magnetic, charge-ordered, and superconducting states including the eta-pairing phase, i.e. the state with the Cooper-pair center-of-mass momentum q = Q. The ground state phase diagrams are obtained for arbitrary particle concentration n on nonfrustrated d = 2 square lattice.
Physical Review B, 2009
We study the thermodynamics of the two-dimensional Hubbard model within the dynamical cluster approximation. We use continuous time quantum Monte Carlo as a cluster solver to avoid the systematic error which complicates the calculation of the entropy and potential energy (double occupancy). We find that at a critical filling, there is a pronounced peak in the entropy divided by temperature, S/T , and in the normalized double occupancy as a function of doping. At this filling, we find that specific heat divided by temperature, C/T , increases strongly with decreasing temperature and kinetic and potential energies vary like T 2 ln T. These are all characteristics of quantum critical behavior.
Thermodynamic properties of a two-site Hubbard model with orbital degeneracy
1979
Exact numerical solutions are obtained for a two-site doubly degenerate Hubbard model with 2, 3 or 4 electrons to study the effect of intra-atomic exchange interaction on the ground state and the thermodynamic properties. Some properties of macroscopic systems are reproduced qualitatively. The condition of having the Hamiltonian rotationally invariant in spin space gets important with increasing electron density.
Phase diagram of the extended hubbard model with pair hopping interaction
The European Physical Journal B-Condensed …, 2002
A one-dimensional model of interacting electrons with on-site U , nearest-neighbor V , and pairhopping interaction W is studied at half-filling using the continuum limit field theory approach. The ground state phase diagram is obtained for a wide range of coupling constants. In addition to the insulating spin-and charge-density wave phases for large U and V , respectively, we identify bond-located ordered phases corresponding to an enhanced Peierls instability in the system for W < 0, |U − 2V | < |2W |, and to a staggered magnetization located on bonds between sites for W > 0, |U − 2V | < W. The general ground state phase diagram including insulating, metallic, and superconducting phases is discussed. A transition to the ηπ-superconducting phase at |U − 2V | ≪ 2t ≤ W is briefly discussed.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2011
Transport measurements on the cuprates suggest the presence of a quantum critical point (QCP) hiding underneath the superconducting dome near optimal hole doping. We provide numerical evidence in support of this scenario via a dynamical cluster quantum Monte Carlo study of the extended two-dimensional Hubbard model. Single-particle quantities, such as the spectral function, the quasi-particle weight and the entropy, display a crossover between two distinct ground states: a Fermi liquid at low filling and a non-Fermi liquid with a pseudo-gap at high filling. Both states are found to cross over to a marginal Fermi-liquid state at higher temperatures. For finite next-nearest-neighbour hopping t ′, we find a classical critical point at temperature T c . This classical critical point is found to be associated with a phase-separation transition between a compressible Mott gas and an incompressible Mott liquid corresponding to the Fermi liquid and the pseudo-gap state, respectively. Since ...
Exact solution of the 1D Hubbard model in the atomic limit with inter-site magnetic coupling
The European Physical Journal B, 2013
In this paper we present for the first time the exact solution in the narrow-band limit of the 1D extended Hubbard model with nearest-neighbour spin-spin interactions described by an exchange constant J. An external magnetic field h is also taken into account. This result has been obtained in the framework of the Green's functions formalism, using the Composite Operator Method. By means of this theoretical background, we have studied some relevant features such as double occupancy, magnetization, spin-spin and charge-charge correlation functions and derived a phase diagram for both ferro (J > 0) and anti-ferro (J < 0) coupling in the limit of zero temperature. We also report a study on density of states, specific heat, charge and spin susceptibilities. In the limit of zero temperature, we show that the model exhibits a very rich phase diagram characterized by different magnetic orders and by the coexistence of charge and spin orderings at commensurate filling. Moreover, our analysis at finite temperature of density of states and response functions shows the presence of low-temperature charge and spin excitations near the phase boundaries.
Arxiv preprint arXiv: …, 2011
In this report we have analyzed a simple effective model for a description of magnetically ordered insulators. The Hamiltonian considered consists of the effective on-site interaction (U ) and the intersite Ising-like magnetic exchange interaction (J) between nearest neighbors. For the first time the phase diagrams of this model have been determined within Monte Carlo simulation on 2D-square lattice. They have been compared with results obtained within variational approach, which treats the on-site term exactly and the intersite interactions within mean-field approximation. We show within both approaches that, depending on the values of interaction parameters and the electron concentration, the system can exhibit not only homogeneous phases: (anti-)ferromagnetic (F) and nonordered (NO), but also phase separated states (PS: F-NO).