Role of Coulomb correlation on magnetic and transport properties of doped manganites: La0.5Sr0.5MnO3 and LaSr2Mn2O7

Results of LSDA and LSDA+U calculations of the electronic structure and magnetic configurations of the 50% hole-doped pseudocubic perovskite La0.5Sr0.5MnO3 and double layered LaSr2Mn2O7 are presented. We demonstrate that the on-site Coulomb correlation (U) of Mn d electrons has a very different influence on the (i) band formations, (ii) magnetic ground states, (iii) interlayer exchange interactions, and (iv) anisotropy of the electrical transport in these two manganites. A possible reason why the LSDA failures in predicting observed magnetic and transport properties of the double layered compound - in contrast to the doped perovskite manganite - is considered on the basis of a p-d hybridization analysis.Comment: 11 pages, 3 figure

Generalized momenta of mass and their applications to the flow of compressible fluid

We present a technique that allows to obtain certain results in the compressible fluid theory: in particular, it is a nonexistence result for the highly decreasing at infinity solutions to the Navier-Stokes equations, the construction of the solutions with uniform deformation and the study of behavior of the boundary of a material volume of liquid.Comment: 10 pages, Proceedings of the International Conference on Hyperbolic Problems, Lyon, 2006, France. In pres

Light hadron production in Bc→Bs(∗)+XB_{c}\to B_{s}^{(*)}+X decays

The article is devoted to Bc->Bs+n pi, Bc->Bs*+n pi decays with n=1, 2, 3, 4. In the framework of factorization theorem the branching fractions of these processes can be written as convolution of hard part, describing Bc->Bs W, Bc->Bs* W vertices, and spectral functions, that correspond to transition of virtual $W$-boson into a final pi-meson system. These functions were obtained from the fit of experimental data on $\tau$-lepton decay and electron-positron annihilation. Using different sets of Bc->Bs decay form-factors we present branching fractions and distributions over the invariant mass of the final pi-meson system.Comment: minor changes, some references adde

Pressure-driven metal-insulator transition in BiFeO3_3 from Dynamical Mean-Field Theory

A metal-insulator transition (MIT) in BiFeO$_3$ under pressure was investigated by a method combining Generalized Gradient Corrected Local Density Approximation with Dynamical Mean-Field Theory (GGA+DMFT). Our paramagnetic calculations are found to be in agreement with experimental phase diagram: Magnetic and spectral properties of BiFeO3 at ambient and high pressures were calculated for three experimental crystal structures $R3c$, $Pbnm$ and $Pm\bar{3}m$. At ambient pressure in the $R3c$ phase, an insulating gap of 1.2 eV was obtained in good agreement with its experimental value. Both $R3c$ and $Pbnm$ phases have a metal-insulator transition that occurs simultaneously with a high-spin (HS) to low-spin (LS) transition. The critical pressure for the $Pbnm$ phase is 25-33 GPa that agrees well with the experimental observations. The high pressure and temperature $Pm\bar{3}m$ phase exhibits a metallic behavior observed experimentally as well as in our calculations in the whole range of considered pressures and undergoes to the LS state at 33 GPa where a $Pbnm$ to $Pm\bar{3}m$ transition is experimentally observed. The antiferromagnetic GGA+DMFT calculations carried out for the $Pbnm$ structure result in simultaneous MIT and HS-LS transitions at a critical pressure of 43 GPa in agreement with the experimental data

Doping-driven Mott transition in La_{1-x}Sr_xTiO_3 via simultaneous electron and hole doping of t2g subbands

The insulator to metal transition in LaTiO_3 induced by La substitution via Sr is studied within multi-band exact diagonalization dynamical mean field theory at finite temperatures. It is shown that weak hole doping triggers a large interorbital charge transfer, with simultaneous electron and hole doping of t2g subbands. The transition is first-order and exhibits phase separation between insulator and metal. In the metallic phase, subband compressibilities become very large and have opposite signs. Electron doping gives rise to an interorbital charge flow in the same direction as hole doping. These results can be understood in terms of a strong orbital depolarization.Comment: 4 pages, 5 figure

Non-leptonic two-body decays of the Bc meson in light-front quark model and QCD factorization approach

We study exclusive non-leptonic two-body $B_c\to(D_{(s)},\eta_c,B_{(s)})+F$ decays with $F$(pseudoscalar or vector meson) being factored out in QCD factorization approach. The non-leptonic decay amplitudes are related to the product of meson decay constants and the form factors for semileptonic $B_c$ decays. As inputs in obtaining the branching ratios for a large set of non-leptonic $B_c$ decays, we use the weak form factors for the semileptonic $B_c\to(D_{(s)},\eta_c,B_{(s)})$ decays in the whole kinematical region and the unmeasured meson decay constants obtained from our previous light-front quark model. We compare our results of the branching ratios with those of other theoretical studies.Comment: 11 pages, 3 figures, minor corrections, version to appear in PR

Post density functional theoretical studies of highly polar semiconductive Pb(Ti1−x_{1-x}Nix_{x})O3−x_{3-x} solid solutions: The effects of cation arrangement on band gap

We use a combination of conventional density functional theory (DFT) and post-DFT methods, including the local density approximation plus Hubbard $U$ (LDA+$U$), PBE0, and self-consistent $GW$ to study the electronic properties of Ni-substituted PbTiO$_{3}$ (Ni-PTO) solid solutions. We find that LDA calculations yield unreasonable band structures, especially for Ni-PTO solid solutions that contain an uninterrupted NiO$_{2}$ layer. Accurate treatment of localized states in transition-metal oxides like Ni-PTO requires post-DFT methods. $B$-site Ni/Ti cation ordering is also investigated. The $B$-site cation arrangement alters the bonding between Ni and O, and therefore strongly affects the band gap ($E_{\rm g}$) of Ni-PTO. We predict that Ni-PTO solid solutions should have a direct band gap in the visible light energy range, with polarization similar to the parent PbTiO$_{3}$. This combination of properties make Ni-PTO solid solutions promising candidate materials for solar energy conversion devices.Comment: 19 pages, 6 figure

Branching ratios of Bc Meson Decays into Tensor Meson in the Final State

Two-body hadronic weak decays of Bc meson involving tensor meson in the final state are studied by using Isgur- Scora-Grinstein-Wise (ISGW II) model. Decay amplitudes are obtained using the factorization scheme in the Spectator Quark Model. Branching ratios for the charm changing and bottom changing decay modes are predicted.Comment: 18 pages. accepted in Physical Review

Visible Effects of the Hidden Sector

The renormalization of operators responsible for soft supersymmetry breaking is usually calculated by starting at some high scale and including only visible sector interactions in the evolution equations, while ignoring hidden sector interactions. Here we explain why this is correct only for the most trivial structures in the hidden sector, and discuss possible implications. This investigation was prompted by the idea of conformal sequestering. In that framework hidden sector renormalizations by nearly conformal dynamics are critical. In the original models of conformal sequestering it was necessary to impose hidden sector flavor symmetries to achieve the sequestered form. We present models which can evade this requirement and lead to no-scale or anomaly mediated boundary conditions; but the necessary structures do not seem generic. More generally, the ratios of scalar masses to gaugino masses, the $\mu$-term, the $B\mu$-term, $A$-terms, and the gravitino mass can be significantly affected.Comment: 23 pages, no figure

Nonmonotonical crossover of the effective susceptibility exponent

We have numerically determined the behavior of the magnetic susceptibility upon approach of the critical point in two-dimensional spin systems with an interaction range that was varied over nearly two orders of magnitude. The full crossover from classical to Ising-like critical behavior, spanning several decades in the reduced temperature, could be observed. Our results convincingly show that the effective susceptibility exponent gamma_eff changes nonmonotonically from its classical to its Ising value when approaching the critical point in the ordered phase. In the disordered phase the behavior is monotonic. Furthermore the hypothesis that the crossover function is universal is supported.Comment: 4 pages RevTeX 3.0/3.1, 5 Encapsulated PostScript figures. Uses epsf.sty. Accepted for publication in Physical Review Letters. Also available as PostScript and PDF file at http://www.tn.tudelft.nl/tn/erikpubs.htm