2,303 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
Metal-Insulator Transition and Lattice Instability of Paramagnetic V2O3
We determine the electronic structure and phase stability of paramagnetic
VO at the Mott-Hubbard metal-insulator phase transition, by employing a
combination of an ab initio method for calculating band structures with
dynamical mean-field theory. The structural transformation associated with the
metal-insulator transition is found to occur upon a slight expansion of the
lattice volume by %, in agreement with experiment. Our results show
that the structural change precedes the metal-insulator transition, implying a
complex interplay between electronic and lattice degrees of freedom at the
transition. Electronic correlations and full charge self-consistency are found
to be crucial for a correct description of the properties of VO.Comment: 5 pages, 4 figure
Electronic Structure and Exchange Interactions of NaVO
We have performed first-principle calculations of the electronic structure
and exchange couplings for the nanotube compound NaVO using
the LDA+U approach. Our results show that while the intra-ring exchange
interactions are mainly antiferromagnetic, the inter-ring couplings are {\it
ferromagnetic}. We argue that this is a consequence of the strong hybridization
between filled and vacant 3d vanadium orbitals due to the low symmetry of
NaVO, which results into strong - and often dominant -
ferromagnetic contributions to the total exchange interaction between vanadium
atoms. A comparison with results of previous works is included.Comment: 6 pages, 5 figure
Differentiation circuits for amplitude modulated signal envelopes
Differentiation circuits for amplitude modulated signal envelope
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
Electronic structure of charge-ordered Fe3O4 from calculated optical, megneto-optical Kerr effect, and O K-edge x-ray absorption spectra
The electronic structure of the low-temperature (LT) monoclinic magnetite,
Fe3O4, is investigated using the local spin density approximation (LSDA) and
the LSDA+U method. The self-consistent charge ordered LSDA+U solution has a
pronounced [001] charge density wave character. In addition, a minor [00{1/2}]
modulation in the phase of the charge order (CO) also occurs. While the
existence of CO is evidenced by the large difference between the occupancies of
the minority spin t_{2g} states of ``2+'' and ``3+'' Fe_B cations, the total 3d
charge disproportion is small, in accord with the valence-bond-sum analysis of
structural data. Weak Fe orbital moments of ~0.07 mB are obtained from
relativistic calculations for the CO phase which is in good agreement with
recent x-ray magnetic circular dichroism measurements. Optical, magneto-optical
Kerr effect, and O K-edge x-ray absorption spectra calculated for the charge
ordered LSDA+U solution are compared to corresponding LSDA spectra and to
available experimental data. Reasonably good agreement between the theoretical
and experimental spectra supports the relevance of the CO solution obtained for
the monoclinic LT phase. The results of calculations of effective exchange
coupling constants between Fe spin magnetic moments are also presented.Comment: 32 pages, 10 figure
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