515 research outputs found
Correlation induced spin freezing transition in FeSe: a dynamical mean field study
The effect of local Coulomb interactions on the electronic properties of FeSe
is explored within dynamical mean field theory combined with finite-temperature
exact diagonalization. The low-energy scattering rate is shown to exhibit
non-Fermi-liquid behavior caused by the formation of local moments.
Fermi-liquid properties are restored at large electron doping. In contrast,
FeAsLaO is shown to be located on the Fermi-liquid side of this spin freezing
transition.Comment: 4 pages, 5 figure
Subband filling and Mott transition in Ca_{2-x}Sr_xRuO_4
A new concept is proposed for the paramagnetic metal insulator transition in
the layer perovskite Ca_{2-x}Sr_xRuO_4. Whereas the pure Sr compound is
metallic up to very large Coulomb energies due to strong orbital fluctuations,
structural changes induced by doping with Ca give rise to a interorbital charge
transfer which makes the material extremely sensitive to local correlations.
Using dynamical mean field theory based on finite temperature multi-band exact
diagonalization it is shown that the combination of crystal field splitting and
onsite Coulomb interactions leads to complete filling of the d_xy band and to a
Mott transition in the half-filled d_xz,yz bands.Comment: 4 pages, 3 figure
Coulomb correlations do not fill the e'_g hole pockets in Na_{0.3}CoO_2
There exists presently considerable debate over the question whether local
Coulomb interactions can explain the absence of the small e'_g Fermi surface
hole pockets in photoemission studies of Na_{0.3}CoO_2. By comparing dynamical
mean field results for different single particle Hamiltonians and exact
diagonalization as well as quantum Monte Carlo treatments, we show that, for
realistic values of the Coulomb energy U and Hund exchange J, the e'_g pockets
can be slightly enhanced or reduced compared to band structure predictions, but
they do not disappear.Comment: 4 pages, 2 figure
Effect of Dynamical Coulomb Correlations on the Fermi Surface of Na_0.3CoO_2
The t2g quasi-particle spectra of Na_0.3CoO_2 are calculated within the
dynamical mean field theory. It is shown that as a result of dynamical Coulomb
correlations charge is transfered from the nearly filled e_g' subbands to the
a_1g band, thereby reducing orbital polarization among Co t2g states. Dynamical
correlations therefore stabilize the small e_g' Fermi surface pockets, in
contrast to angle-resolved photoemission data, which do not reveal these
pockets.Comment: 4 pages, to appear in PR
Mott transition in two-dimensional frustrated compounds
The phase diagrams of isotropic and anisotropic triangular lattices with
local Coulomb interactions are evaluated within cluster dynamical mean field
theory. As a result of partial geometric frustration in the anisotropic
lattice, short range correlations are shown to give rise to reentrant behavior
which is absent in the fully frustrated isotropic limit. The qualitative
features of the phase diagrams including the critical temperatures are in good
agreement with experimental data for the layered organic charge transfer salts
kappa-(BEDT-TTF)_2Cu[N(CN)_2]Cl and kappa-(BEDT-TTF)_2Cu_2(CN)_3.Comment: 4 pages, 4 figure
Coulomb blockade and Kondo effect in the electronic structure of Hubbard molecules connected to metallic leads: a finite-temperature exact-diagonalization study
The electronic structure of small Hubbard molecules coupled between two
non-interacting semi-infinite leads is studied in the low bias-voltage limit.
To calculate the finite-temperature Green's function of the system, each lead
is simulated by a small cluster, so that the problem is reduced to that of a
finite-size system comprising the molecule and clusters on both sides. The
Hamiltonian parameters of the lead clusters are chosen such that their
embedding potentials coincide with those of the semi-infinite leads on
Matsubara frequencies. Exact diagonalization is used to evaluate the effect of
Coulomb correlations on the electronic properties of the molecule at finite
temperature. Depending on key Hamiltonian parameters, such as Coulomb
repulsion, one-electron hopping within the molecule, and hybridization between
molecule and leads, the molecular self-energy is shown to exhibit Fermi-liquid
behavior or deviations associated with finite low-energy scattering rates. The
method is shown to be sufficiently accurate to describe the formation of Kondo
resonances inside the correlation-induced pseudogaps, except in the limit of
extremely low temperatures. These results demonstrate how the system can be
tuned between the Coulomb blockade and Kondo regimes.Comment: 14 pages; 14 figure
Embedding approach for dynamical mean field theory of strongly correlated heterostructures
We present an embedding approach based on localized basis functions which
permits an efficient application of the dynamical mean field theory (DMFT) to
inhomogeneous correlated materials, such as semi-infinite surfaces and
heterostructures. In this scheme, the semi-infinite substrate leads connected
to both sides of the central region of interest are represented via complex,
energy-dependent embedding potentials that incorporate one-electron as well as
many-body effects within the substrates. As a result, the number of layers
which must be treated explicitly in the layer-coupled DMFT equation is greatly
reduced. To illustrate the usefulness of this approach, we present numerical
results for strongly correlated surfaces, interfaces, and heterostructures of
the single-band Hubbard model.Comment: 8 pages, 4 figures; typos correcte
First-principles calculation of field emission from metal surfaces
The field-emission current from realistic metal surfaces is evaluated within the density-functional theory using the Landauer-Buttiker approach. The electronic density in the surface region and the potential barrier induced by the finite electric field are calculated self-consistently using a Green's-function embedding scheme and the full-potential linearized-augmented plane-wave method. Application of this formalism to the (100) and (111) faces of Au and Cu demonstrates the sensitivity of the field-emission current to the surface electronic structure close to the Fermi energy
The Mott insulator LaTiO_3 in heterostructures with SrTiO_3 is metallic
It is shown that LaTiO_3 in superlattices with SrTiO_3 is not a Mott
insulator but a strongly correlated metal. The tetragonal lattice geometry
imposed by the SrTiO_3 substrate leads to an increase of the Ti 3d t2g band
width and a reversal of the t2g crystal field relative to the orthorhombic bulk
geometry. Using dynamical mean field theory based on finite-temperature
multi-band exact diagonalization we show that, as a result of these effects,
local Coulomb interactions are not strong enough to induce a Mott transition in
tetragonal LaTiO_3. The metalicity of these heterostructures is therefore not
an interface property but stems from all LaTiO_3 planes.Comment: 4 pages, 4 figure
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