2,474 research outputs found
Single Mott Transition in Multi-Orbital Hubbard Model
The Mott transition in a multi-orbital Hubbard model involving subbands of
different widths is studied within the dynamical mean field theory. Using the
iterated perturbation theory for the quantum impurity problem it is shown that
at low temperatures inter-orbital Coulomb interactions give rise to a single
first-order transition rather than a sequence of orbital selective transitions.
Impurity calculations based on the Quantum Monte Carlo method confirm this
qualitative behavior. Nevertheless, at finite temperatures, the degree of
metallic or insulating behavior of the subbands differs greatly. Thus, on the
metallic side of the transition, the narrow band can exhibit quasi-insulating
features, whereas on the insulating side the wide band exhibits pronounced
bad-metal behavior. This complexity might partly explain contradictory results
between several previous works.Comment: 8 pages, 11 figure
Theory of optically forbidden d-d transitions in strongly correlated crystals
A general multiband formulation of linear and non-linear optical response
functions for realistic models of correlated crystals is presented. Dipole
forbidden d-d optical transitions originate from the vertex functions, which we
consider assuming locality of irreducible four-leg vertex. The unified
formulation for second- and third-order response functions in terms of the
three-leg vertex is suitable for practical calculations in solids. We
illustrate the general approach by consideration of intraatomic spin-flip
contributions, with the energy of 2J, where J is a Hund exchange, in the
simplest two-orbital model.Comment: 9 pages, 4 figures, to appear in J. Phys. Cond. Matte
Nonlocal correlations in the vicinity of the - phase transition in iron within a DMFT plus spin-fermion model approach
We consider nonlocal correlations in iron in the vicinity of the
- phase transition within the spin-rotationally-invariant
dynamical mean-field theory (DMFT) approach, combined with the recently
proposed spin-fermion model of iron. The obtained nonlocal corrections to DMFT
yield a decrease of the Curie temperature of the phase, leading to an
agreement with its experimental value. We show that the corresponding nonlocal
corrections to the energy of the phase are crucially important to
obtain the proximity of energies of and phases in the
vicinity of the iron - transformation.Comment: 5 pages, 2 figure
Effect of density of states peculiarities on Hund's metal behavior
We investigate a possibility of Hund's metal behavior in the Hubbard model
with asymmetric density of states having peak(s). Specifically, we consider the
degenerate two-band model and compare its results to the five-band model with
realistic density of states of iron and nickel, showing that the obtained
results are more general, provided that the hybridization between states of
different symmetry is sufficiently small. We find that quasiparticle damping
and the formation of local magnetic moments due to Hund's exchange interaction
are enhanced by both, the density of states asymmetry, which yields stronger
correlated electron or hole excitations, and the larger density of states at
the Fermi level, increasing the number of virtual electron-hole excitations.
For realistic densities of states these two factors are often interrelated
because the Fermi level is attracted towards peaks of the density of states. We
discuss the implication of the obtained results to various substances and
compounds, such as transition metals, iron pnictides, and cuprates.Comment: 7 pages, 7 figure
First-principles Calculations of the Electronic Structure and Spectra of Strongly Correlated Systems: Dynamical Mean-field Theory
A recently developed dynamical mean-field theory in the iterated perturbation
theory approximation was used as a basis for construction of the "first
principles" calculation scheme for investigating electronic structure of
strongly correlated electron systems. This scheme is based on Local Density
Approximation (LDA) in the framework of the Linearized Muffin-Tin-Orbitals
(LMTO) method. The classical example of the doped Mott-insulator
La_{1-x}Sr_xTiO_3 was studied by the new method and the results showed
qualitative improvement in agreement with experimental photoemission spectra.Comment: 11 pages, 3 Postscript figures, LaTeX, submit in Journal of Physics:
Condensed Matte
Momentum-dependent susceptibilities and magnetic exchange in bcc iron from supercell DMFT calculations
We analyze the momentum- and temperature dependences of the magnetic
susceptibilities and magnetic exchange interaction in paramagnetic bcc iron by
a combination of density functional theory and dynamical mean-field theory
(DFT+DMFT). By considering a general derivation of the orbital-resolved
effective model for spin degrees of freedom for Hund's metals, we relate
momentum-dependent susceptibilities in the paramagnetic phase to the magnetic
exchange. We then calculate non-uniform orbital-resolved susceptibilities at
high-symmetry wave vectors by constructing appropriate supercells in the DMFT
approach. Extracting the irreducible parts of susceptibilities with respect to
Hund's exchange interaction, we determine the corresponding orbital-resolved
exchange interactions, which are then interpolated to the whole Brillouin zone.
Using the spherical model we estimate the temperature dependence of the
resulting exchange between local moments.Comment: 18 pages, 6 figure
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