1,019 research outputs found
Equation of motion approach to the Hubbard model in infinite dimensions
We consider the Hubbard model on the infinite-dimensional Bethe lattice and
construct a systematic series of self-consistent approximations to the
one-particle Green's function, . The first
equations of motion are exactly fullfilled by and the
'th equation of motion is decoupled following a simple set of decoupling
rules. corresponds to the Hubbard-III approximation. We
present analytic and numerical results for the Mott-Hubbard transition at half
filling for .Comment: 10pager, REVTEX, 8-figures not available in postscript, manuscript
may be understood without figure
Zero-temperature magnetism in the periodic Anderson model in the limit of large dimensions
We study the magnetism in the periodic Anderson model in the limit of large
dimensions by mapping the lattice problem into an equivalent local impurity
self-consistent model. Through a recently introduced algorithm based on the
exact diagonalization of an effective cluster hamiltonian, we obtain solutions
with and without magnetic order in the half-filled case. We find the exact
AFM-PM phase boundary which is shown to be of order and obeys
We calculate the local staggered moments and the
density of states to gain insights on the behavior of the AFM state as it
evolves from itinerant to a local-moment magnetic regimeComment: 9 pages + 9 figures, to appear in Phys. Rev. B, 1 Sept. 1995 issu
Effects of degenerate orbitals on the Hubbard model
Stability of a metallic state in the two-orbital Hubbard model at
half-filling is investigated. We clarify how spin and orbital fluctuations are
enhanced to stabilize the formation of quasi-particles by combining dynamical
mean field theory with the quantum Monte Carlo simulations. These analyses shed
some light on the reason why the metallic phase is particularly stable when the
intra- and inter-band Coulomb interactions are nearly equal.Comment: 3 pages, To appear in JPSJ Vol. 72, No. 5 200
Mott transition at large orbital degeneracy: dynamical mean-field theory
We study analytically the Mott transition of the N-orbital Hubbard model
using dynamical mean-field theory and a low-energy projection onto an effective
Kondo model. It is demonstrated that the critical interaction at which the
insulator appears (Uc1) and the one at which the metal becomes unstable (Uc2)
have different dependence on the number of orbitals as the latter becomes
large: Uc1 ~ \sqrt{N} while Uc2 ~ N. An exact analytical determination of the
critical coupling Uc2/N is obtained in the large-N limit. The metallic solution
close to this critical coupling has many similarities at low-energy with the
results of slave boson approximations, to which a comparison is made. We also
discuss how the critical temperature associated with the Mott critical endpoint
depends on the number of orbitals.Comment: 13 pages. Minor changes in V
Transfer of Spectral Weight in Spectroscopies of Correlated Electron Systems
We study the transfer of spectral weight in the photoemission and optical
spectra of strongly correlated electron systems. Within the LISA, that becomes
exact in the limit of large lattice coordination, we consider and compare two
models of correlated electrons, the Hubbard model and the periodic Anderson
model. The results are discussed in regard of recent experiments. In the
Hubbard model, we predict an anomalous enhancement optical spectral weight as a
function of temperature in the correlated metallic state which is in
qualitative agreement with optical measurements in . We argue that
anomalies observed in the spectroscopy of the metal are connected to the
proximity to a crossover region in the phase diagram of the model. In the
insulating phase, we obtain an excellent agreement with the experimental data
and present a detailed discussion on the role of magnetic frustration by
studying the resolved single particle spectra. The results for the periodic
Anderson model are discussed in connection to recent experimental data of the
Kondo insulators and . The model can successfully explain
the different energy scales that are associated to the thermal filling of the
optical gap, which we also relate to corresponding changes in the density of
states. The temperature dependence of the optical sum rule is obtained and its
relevance for the interpretation of the experimental data discussed. Finally,
we argue that the large scattering rate measured in Kondo insulators cannot be
described by the periodic Anderson model.Comment: 19 pages + 29 figures. Submitted to PR
The Metal-Insulator Transition in the Doubly Degenerate Hubbard Model
A systematic study has been made on the metal-insulator (MI) transition of
the doubly degenerate Hubbard model (DHM) in the paramagnetic ground state, by
using the slave-boson mean-field theory which is equivalent to the Gutzwiller
approximation (GA). For the case of infinite electron-electron interactions, we
obtain the analytic solution, which becomes exact in the limit of infinite
spatial dimension. On the contrary, the finite-interaction case is investigated
by numerical methods with the use of the simple-cubic model with the
nearest-neighbor hopping. The mass-enhancement factor, , is shown to
increase divergently as one approaches the integer fillings (), at
which the MI transition takes place, being the total number of electrons.
The calculated dependence of is compared with the observed
specific-heat coefficient, , of which is reported
to significantly increase as approaches unity.Comment: Latex 16 pages, 10 ps figures included, published in J. Phys. Soc.
Jpn. with some minor modifications. ([email protected]
Magnetooptical sum rules close to the Mott transition
We derive new sum rules for the real and imaginary parts of the
frequency-dependent Hall constant and Hall conductivity. As an example, we
discuss their relevance to the doped Mott insulator that we describe within the
dynamical mean-field theory of strongly correlated electron systems.Comment: 4 pages, 4 ps figures; accepted for publication in PR
Fuzzy splicing systems
In this paper we introduce a new variant of splicing systems, called fuzzy splicing systems, and establish some basic properties of language families generated by this type of splicing systems. We study the “fuzzy effect” on splicing operations, and show that the “fuzzification” of splicing systems can increase and decrease the computational power of splicing systems with finite components with respect to fuzzy operations and cut-points chosen for threshold languages
Dynamical Mean Field Theory of the Antiferromagnetic Metal to Antiferromagnetic Insulator Transition
We study the antiferromagnetic metal to antiferromagnetic insulator using
dynamical mean field theory and exact diagonalization methods. We find two
qualitatively different behaviors depending on the degree of magnetic
correlations. For strong correlations combined with magnetic frustration, the
transition can be described in terms of a renormalized slater theory, with a
continuous gap closure driven by the magnetism but strongly renormalized by
correlations. For weak magnetic correlations, the transition is weakly first
order.Comment: 4 pages, uses epsfig,4 figures,notational errors rectifie
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