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

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

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

Phase Transition in Hot Pion Matter

The equation of state for the pion gas is analyzed within the third virial approximation. The second virial coefficient is found from the pion-pion- scattering data, while the third one is considered as a free parameter. The proposed model leads to a first-order phase transition from the pion gas to a more dense phase at the temperature T_pt < 136 MeV. Due to relatively low temperature this phase transition cannot be related to the deconfinement. This suggests that a new phase of hadron matter - 'hot pion liquid' - may exist.Comment: 11 pages, Latex, 4 PS-figures. V2: A few misprints are corrected. Acknowledgments are adde

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

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