Symmetries and Mean-Field Phases of the Extended Hubbard Model

Abstract

The two-dimensional extended Hubbard model that includes a nearest- neighbor Heisenberg interaction is studied using a mean-field theory where quasiparticles are defined by an U(8) group of canonical transformations. The theory is a generalization of the ordinary BCS theory, and Balian and Werthamer's theory of He-3 that permits both broken gauge, spin and sublattice symmetry. This allows us to investigate superconductivity, antiferromagnetic order, charge density waves and, by twisting the spin quantization axis, spiral antiferromagnetic order in the same theory. Our results for positive Hubbard U and Heisenberg exchange J suggest that antiferromagnetic ordering dominates close to half filling, while spiral states and d-wave superconductivity compete when doping is introduced. For moderate values of J, we find a phase diagram where a phase transition occurs from an antiferromagnet to a d-wave superconductor as doping is increased. A narrow region of (s+id)-wave superconductor is found for some values of J and U.

Revtex, 27 pages, 8 figures uuencoded with uufiles. Replaced because (s+id)-wave superconductivity is found (not (s+d)-wave)

References in corpus (4)

• New Exactly Solvable Model of Strongly Correlated Electrons Motivated by High T_c Superconductivity
• Generalized Hartree-Fock Theory and the Hubbard Model
• $\eta$-pairing as a mechanism of superconductivity in models of strongly correlated electrons
• Superconductivity in an exactly solvable Hubbard model with bond-charge interaction

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• Exact Transformation for Spin-Charge Separation of Spin-half Fermions without Constraints
• Mean-field phase diagram of the Bose-Fermi Hubbard model
• The quantum critical behavior of antiferromagnetic itinerant systems with van Hove singularities of electronic spectrum
• Collective excitations in competing phases in two and three dimensions
• Spinon and eta-spinon correlation functions
• Fictitious fluxes in doped antiferromagnets
• Spin density wave selection in the one-dimensional Hubbard model
• Nonlocal Exchange Interactions in Strongly Correlated Electron Systems