PHASE DIAGRAM OF STRIPE ORDER IN THE EXTENDED HUBBARD MODEL

2000 ◽  
Vol 14 (29n31) ◽  
pp. 3508-3513 ◽  
Author(s):  
MASARU KATO
Keyword(s):  
Hubbard Model ◽  
Coulomb Interaction ◽  
Nearest Neighbor ◽  
Mean Field ◽  
Field Approximation ◽  
Square Lattice ◽  
Mean Field Approximation ◽  
Extended Hubbard Model ◽  
Stable States ◽  
Stripe Order

The extended Hubbard model with the nearest-neighbor Coulomb interaction on the square lattice is studied within the mean-field approximation. The stable states for 8×8 sites lattice with the periodic boundary condition and the electron filling n=0.875, as well as for 10×10 lattice and n=0.80, are obtained. For 8×8 lattice where quarter-filled straight stripe is expected because of the long-range Coulomb interaction, the cross stripe phases become stable.

SUPERCONDUCTING CLASSES IN THE EXTENDED HUBBARD MODEL

1996 ◽  
Vol 10 (12) ◽  
pp. 1397-1423 ◽  
Author(s):  
MASA-AKI OZAKI ◽  
EIJI MIYAI ◽  
TOMOAKI KONISHI ◽  
KAORU HANAFUSA
Keyword(s):  
Hubbard Model ◽  
Nearest Neighbor ◽  
Mean Field ◽  
Square Lattice ◽  
Extended Hubbard Model ◽  
S Wave ◽  
Ferromagnetic Order ◽  
Numerical Studies ◽  
The Mean

This paper describes group theoretical classification of superconducting states (SC) in the extended Hubbard model with on-site repulsion (U), nearest neighbor attraction (V) and nearest neighbour exchange interaction (J) on the two-dimensional square lattice using the mean field approach. By decomposing the pairing interaction into irreducible parts; A1g, B1g and Eu of D4h point symmetry, we have derived two singlet SCs (s-wave and d-wave) from A1g and B1g, eight triplet SCs from Eu. The first three types of triplet SC have pairing by electrons with antiparallel spin, the second two types have pairing by electrons with equal spin and the last three types are non-unitary and have pairing by only up-spin electrons. We showed that three non-unitary states have to be accompanied with a ferromagnetic order from the structure of the maximal little groups. We performed numerical studies for these SCs. For parameters and electron density favorable for the ferromagnetic order, a non-unitary SC coexistent with ferromagnetism is most stable.

scholarly journals SUPERCONDUCTING ORDER PARAMETERS IN THE EXTENDED HUBBARD MODEL: A SIMPLE MEAN-FIELD STUDY

2007 ◽  
Vol 21 (13n14) ◽  
pp. 2371-2383 ◽  
Author(s):  
J. S. THAKUR ◽  
M. P. DAS
Keyword(s):  
Hubbard Model ◽  
Nearest Neighbor ◽  
Mean Field ◽  
Order Parameters ◽  
Square Lattice ◽  
Extended Hubbard Model ◽  
Self Consistent ◽  
Frame Work ◽  
Field Formalism ◽  
Superconducting Pairing

The extended Hubbard model with nearest neighbor hopping and intersite interaction for a 2D square lattice has been studied within the frame work of a simple mean-field formalism. The self-consistent solutions of superconducting order parameters have been obtained for various fillings. The results indicate that superconducting pairing occurs on doping for the repulsive on-site U and attractive nearest neighbor V.

scholarly journals On the Validity of the Dynamical Mean-Field Approximation for Studying the Two-Dimensional Hubbard Model on a Square Lattice

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
A. N. Ribeiro ◽  
C. A. Macedo
Keyword(s):  
Hubbard Model ◽  
Quantum Monte Carlo ◽  
Mean Field ◽  
Field Approximation ◽  
Square Lattice ◽  
Mean Field Approximation ◽  
Two Dimensional ◽  
Infinite Dimensions ◽  
Antiferromagnetic Correlations ◽  
Half Filling

The dynamical mean-field approximation (DMFA) becomes exact in the limit of infinite dimensions, and allows results to be obtained in a nonperturbative regime without the limitations normally found with exact diagonalization (ED) and quantum Monte Carlo (QMC) methods. In this paper, we investigate the applicability of the method to lattices with small coordination number in special situations. Specifically we use this approximation to study the two-dimensional (2D) Hubbard model on a square lattice far from half filling. In this situation, we calculate the specific heat and find that when the filling decreases, that is, antiferromagnetic correlations become less important, the agreement between DMFA and QMC results increases. Our results show that the DMFA can be a valuable technique for studying the thermodynamic properties of the Hubbard model also on a square lattice, but within a parameter range in which the antiferromagnetic correlations are not important.

scholarly journals Энергетический спектр и оптические свойства фуллерена C-=SUB=-80-=/SUB=-(I-=SUB=-h-=/SUB=-) в модели Хаббарда

2021 ◽  
Vol 129 (10) ◽  
pp. 1227
Author(s):  
А.В. Силантьев
Keyword(s):  
Group Theory ◽  
Hubbard Model ◽  
Symmetry Group ◽  
Mean Field ◽  
Analytical Form ◽  
Field Approximation ◽  
Energy Spectra ◽  
Mean Field Approximation ◽  
The Mean

The anticommutative Green’s functions were derived in an analytical form, and the energy spectra of С80 fullerene and endohedral Y3N@C80 fullerene of symmetry group Ih were obtained within the Hubbard model in the mean-field approximation. Using group theory methods, the classification of energy states was carried out, and the allowed transitions in the energy spectra of С80 and Y3N@C80 molecules of symmetry group Ih were determined.

POSSIBLE COEXISTENCE OF ANTIFERROMAGNETISM AND SUPERCONDUCTIVITY IN THE HUBBARD MODEL

1988 ◽  
Vol 01 (09n10) ◽  
pp. 341-347 ◽  
Author(s):  
SHEN JUE-LIAN ◽  
SU ZHAO-BIN ◽  
DONG JIN-MING ◽  
YU LU
Keyword(s):  
Hubbard Model ◽  
High Temperature Superconductivity ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Antiferromagnetic Order ◽  
Effective Hamiltonian ◽  
Hamiltonian Approach ◽  
Theoretical Approaches ◽  
The Mean

The Hubbard model in the nearly half-filled case was studied in the mean field approximation using the effective Hamiltonian approach. Both antiferromagnetic order parameter and condensation of singlet pairs were considered. In certain parameter range the coexistence of antiferromagnetism and superconductivity is energetically favorable. Relations to the high temperature superconductivity and other theoretical approaches are also discussed.

GROUND STATE OF THE 2D EXTENDED HUBBARD MODEL WITH MORE THAN NEAREST-NEIGHBOR INTERACTIONS

2012 ◽  
Vol 26 (29) ◽  
pp. 1250156 ◽  
Author(s):  
S. HARIR ◽  
M. BENNAI ◽  
Y. BOUGHALEB
Keyword(s):  
Phase Diagram ◽  
Hubbard Model ◽  
Ground State ◽  
State Energy ◽  
Nearest Neighbor ◽  
Finite Size ◽  
Square Lattice ◽  
Extended Hubbard Model ◽  
Eigenvalues And Eigenvectors ◽  
Repulsion Energy

We investigate the ground state phase diagram of the two dimensional Extended Hubbard Model (EHM) with more than Nearest-Neighbor (NN) interactions for finite size system at low concentration. This EHM is solved analytically for finite square lattice at one-eighth filling. All eigenvalues and eigenvectors are given as a function of the on-site repulsion energy U and the off-site interaction energy Vij. The behavior of the ground state energy exhibits the emergence of phase diagram. The obtained results clearly underline that interactions exceeding NN distances in range can significantly influence the emergence of the ground state conductor–insulator transition.

scholarly journals ISOSPIN LATTICE GAS MODEL AND NUCLEAR-MATTER PHASE DIAGRAM AND PRESSURE-VOLUME ISOTHERMS

1996 ◽  
Vol 05 (02) ◽  
pp. 303-311 ◽  
Author(s):  
T.T.S. KUO ◽  
S. RAY ◽  
J. SHAMANNA ◽  
R.K. SU
Keyword(s):  
Nuclear Matter ◽  
Lattice Gas ◽  
Nearest Neighbor ◽  
Mean Field ◽  
Field Approximation ◽  
Lattice Gas Model ◽  
Mean Field Approximation ◽  
Kinetic Energy Term ◽  
Phase Liquid ◽  
Matter Phase

We study a cubic lattice gas model for nuclear matter where each lattice site can be either occupied, by one proton or one neutron, or unoccupied. A nearest-neighbor interaction of the form - ∑<ij>Jijτziτzj is assumed. Our model is an isospin-1 Ising model, with τz= (1, 0, –1) representing respectively (proton, vacancy, neutron). A kinetic-energy term has been included in our model. Under the Bragg-Williams mean-field approximation our model exhibits the existence of a dense phase (liquid-like) and a rare phase (gas-like). The nuclear-matter p−v isotherms given by our model are discussed.

PHASE TRANSITIONS OF THE MIXED-SPIN ISING MODEL ON A DECORATED LATTICE WITH THE NEAREST-NEIGHBOR INTERACTION BETWEEN DECORATING SPINS

2009 ◽  
Vol 23 (24) ◽  
pp. 4963-4976 ◽  
Author(s):  
A. BENYOUSSEF ◽  
A. EL KENZ ◽  
M. EL YADARI ◽  
M. LOULIDI
Keyword(s):  
Phase Transitions ◽  
Ising Model ◽  
Phase Diagrams ◽  
Nearest Neighbor ◽  
Mean Field ◽  
Nearest Neighbors ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Neighbor Interaction ◽  
Mixed Spin

A mean-field approximation is developed for a decorated ferrimagnetic Ising model, in which the two magnetic atoms A and B have spins σ=1/2 and S=1, respectively. In this system, the exchange interaction between nearest-neighbors of atom B is taken into account. Some interesting phenomena, such as the appearance of three types of phase diagrams and the existence of one and two compensation points are found. Phase diagrams and temperature dependence of the magnetizations of the system are investigated in detail.

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