11 research outputs found
Electronic correlations and competing orders in multiorbital dimers: a cluster DMFT study
We investigate the violation of the first Hund's rule in 4 and 5
transition metal oxides that form solids of dimers. Bonding states within these
dimers reduce the magnetization of such materials. We parametrize the dimer
formation with realistic hopping parameters and find not only regimes, where
the system behaves as a Fermi liquid or as a Peierls insulator, but also
strongly correlated regions due to Hund's coupling and its competition with the
dimer formation. The electronic structure is investigated using the cluster
dynamical mean-field theory for a dimer in the two-plane Bethe lattice with two
orbitals per site and -filling, that is three electrons per dimer. It
reveals dimer-antiferromagnetic order of a high-spin (double exchange) state
and a low-spin (molecular orbital) state. At the crossover region we observe
the suppression of long-range magnetic order, fluctuation enhancement and
renormalization of electron masses. At certain interaction strengths the system
becomes an incoherent antiferromagnetic metal with well defined local moments.Comment: 11 pages, 10 figure
Valence-band satellite in the ferromagnetic nickel: LDA+DMFT study with exact diagonalization
The valence-band spectrum of the ferromagnetic nickel is calculated using the
LDA+DMFT method. The auxiliary impurity model emerging in the course of the
calculations is discretized and solved with the exact diagonalization, or, more
precisely, with the Lanczos method. Particular emphasis is given to spin
dependence of the valence-band satellite that is observed around 6 eV below the
Fermi level. The calculated satellite is strongly spin polarized in accord with
experimental findings.Comment: REVTeX 4, 8 pages, 5 figure
Effect of Crystal-Field Splitting and Inter-Band Hybridization on the Metal-Insulator Transitions of Strongly Correlated Systems
We investigate a quarter-filled two-band Hubbard model involving a
crystal-field splitting, which lifts the orbital degeneracy as well as an
inter-orbital hopping (inter-band hybridization). Both terms are relevant to
the realistic description of correlated materials such as transition-metal
oxides. The nature of the Mott metal-insulator transition is clarified and is
found to depend on the magnitude of the crystal-field splitting. At large
values of the splitting, a transition from a two-band to a one-band metal is
first found as the on-site repulsion is increased and is followed by a Mott
transition for the remaining band, which follows the single-band
(Brinkman-Rice) scenario well documented previously within dynamical mean-field
theory. At small values of the crystal-field splitting, a direct transition
from a two-band metal to a Mott insulator with partial orbital polarization is
found, which takes place simultaneously for both orbitals. This transition is
characterized by a vanishing of the quasiparticle weight for the majority
orbital but has a first-order character for the minority orbital. It is pointed
out that finite-temperature effects may easily turn the metallic regime into a
bad metal close to the orbital polarization transition in the metallic phase.Comment: 12 pages, 10 figures One figure added. Text revised according to PRB
proof. Appear in PRB 7
Unexpected 3+valence of iron in FeO2, a geologically important material lying "in between" oxides and peroxides
Recent discovery of pyrite FeO, which can be an important ingredient of
the Earth's lower mantle and which in particular may serve as an extra source
of water in the Earth's interior, opens new perspectives for geophysics and
geochemistry, but this is also an extremely interesting material from physical
point of view. We found that in contrast to naive expectations Fe is nearly 3+
in this material, which strongly affects its magnetic properties and makes it
qualitatively different from well known sulfide analogue - FeS. Doping,
which is most likely to occur in the Earth's mantle, makes FeO much more
magnetic. In addition we show that unique electronic structure places FeO
"in between" the usual dioxides and peroxides making this system interesting
both for physics and solid state chemistry
Enhanced Crystal Field Splitting and Orbital Selective Coherence by Strong Correlations in V_2O_3
We present a study of the paramagnetic metallic and insulating phases of
vanadium sesquioxide by means of the th order muffin-tin orbital
implementation of density functional theory combined with dynamical mean-field
theory. The transition is shown to be driven by a correlation-induced
enhancement of the crystal field splitting within the manifold, which
results in a suppression of the hybridization between the and
bands. We discuss the changes in the effective quasi-particle band
structure caused by the correlations and the corresponding self-energies. At
temperatures of about 400 K we find the orbitals to display coherent
quasi-particle behavior, while a large imaginary part of the self-energy and
broad features in the spectral function indicate that the orbitals
are still far above their coherence temperature. The local spectral functions
are in excellent agreement with recent bulk sensitive photoemission data.
Finally, we also make a prediction for angle-resolved photoemission experiments
by calculating momentum-resolved spectral functions.Comment: Paper I will appear in condmat in two week