272 research outputs found
Equivalence of Gutzwiller and slave-boson mean-field theories for multi-band Hubbard models
We demonstrate that a recently introduced slave-boson mean-field theory is
equivalent to our Gutzwiller theory for multi-band Hubbard models with general
onsite interactions. We relate the different objects that appear in both
approaches at zero temperature and discuss the limitations of both methods.Comment: 4 page
Antiferromagnetic order in multi-band Hubbard models for iron-pnictides
We investigate multi-band Hubbard models for the three iron 3-
bands and the two iron 3- bands in by means of the
Gutzwiller variational theory. Our analysis of the paramagnetic ground state
shows that neither Hartree--Fock mean-field theories nor effective spin models
describe these systems adequately. In contrast to Hartree--Fock-type
approaches, the Gutzwiller theory predicts that antiferromagnetic order
requires substantial values of the local Hund's-rule exchange interaction. For
the three-band model, the antiferromagnetic moment fits experimental data for a
broad range of interaction parameters. However, for the more appropriate
five-band model, the iron electrons polarize the electrons and
they substantially contribute to the ordered moment.Comment: 4 pages, 4 figure
Time-Dependent Gutzwiller Theory for Multiband Hubbard Models
Based on the variational Gutzwiller theory, we present a method for the
computation of response functions for multiband Hubbard models with general
local Coulomb interactions. The improvement over the conventional random-phase
approximation is exemplified for an infinite-dimensional two-band Hubbard model
where the incorporation of the local multiplet-structure leads to a much larger
sensitivity of ferromagnetism on the Hund coupling. Our method can be
implemented into LDA+Gutzwiller schemes and will therefore be an important tool
for the computation of response functions for strongly correlated materials.Comment: 4 pages, 3 figure
Gutzwiller description of non-magnetic Mott insulators: a dimer lattice model
We introduce a novel extension of the Gutzwiller variational wavefunction
able to deal with insulators that escape any mean-field like description, as
for instance non-magnetic insulators. As an application, we study the Mott
transition from a paramagnetic metal into a non-magnetic Peierls, or
valence-bond, Mott insulator. We analyze this model by means of our Gutzwiller
wavefunction analytically in the limit of large coordination lattices, where we
find that: (1) the Mott transition is first order; (2) the Peierls gap is large
in the Mott insulator, although it is mainly contributed by the electron
repulsion; (3) singlet-superconductivity arises around the transition.Comment: 15 pages, 9 figure
Coexistence of spin-triplet superconductivity with magnetism within a single mechanism for orbitally degenerate correlated electrons: Statistically-consistent Gutzwiller approximation
An orbitally degenerate two-band Hubbard model is analyzed with inclusion of
the Hund's rule induced spin-triplet paired states and their coexistence with
magnetic ordering. The so-called statistically consistent Gutzwiller
approximation (SGA) has been applied to the case of a square lattice. The
superconducting gaps, the magnetic moment, and the free energy are analyzed as
a function of the Hund's rule coupling strength and the band filling. Also, the
influence of the intersite hybridization on the stability of paired phases is
discussed. In order to examine the effect of correlations the results are
compared with those calculated earlier within the Hartree-Fock (HF)
approximation combined with the Bardeen-Cooper-Schrieffer (BCS) approach.
Significant differences between the two used methods (HF+BCS vs. SGA+real-space
pairing) appear in the stability regions of the considered phases. Our results
supplement the analysis of this canonical model used widely in the discussions
of pure magnetic phases with the detailed elaboration of the stability of the
spin-triplet superconducting states and the coexistent magnetic-superconducting
states. At the end, we briefly discuss qualitatively the factors that need to
be included for a detailed quantitative comparison with the corresponding
experimental results
The Generalized Gutzwiller Method for n=>2 Correlated Orbitals: Itinerant Ferromagnetism in eg-bands
Using the generalized Gutzwiller method we present results on the
ferromagnetic behavior of extended Hubbard models with two degenerate eg
orbitals. We find significant differences to results obtained from Hartree-Fock
theory.Comment: 7 pages in Latex, 3 figures. Accepted for publication in Physica
Gutzwiller theory of band magnetism in LaOFeAs
We use the Gutzwiller variational theory to calculate the ground-state phase
diagram and quasi-particle bands of LaOFeAs. The Fe3d--As4p Wannier-orbital
basis obtained from density-functional theory defines the band part of our
eight-band Hubbard model. The full atomic interaction between the electrons in
the iron orbitals is parameterized by the Hubbard interaction U and an average
Hund's-rule interaction J. We reproduce the experimentally observed small
ordered magnetic moment over a large region of (U,J) parameter space. The
magnetically ordered phase is a stripe spin-density wave of quasi-particles.Comment: 4 pages, 5 figure
Hybridisation in two-band Hubbard models with different bandwidths
We investigate the orbital selective Mott transition in two-band Hubbard
models by means of the Gutzwiller variational theory. In particular, we study
the influence of a finite local hybridisation between electrons in different
orbitals on the metal-insulator transition.Comment: 11 pages, 12 figures, submitted to Journal of Physics: Condensed
Matte
Gutzwiller variational theory for the Hubbard model with attractive interaction
We investigate the electronic and superconducting properties of a negative-U
Hubbard model. For this purpose we evaluate a recently introduced variational
theory based on Gutzwiller-correlated BCS wave functions. We find significant
differences between our approach and standard BCS theory, especially for the
superconducting gap. For small values of , we derive analytical
expressions for the order parameter and the superconducting gap which we
compare to exact results from perturbation theory.Comment: 10 pages, 2 figure
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