727 research outputs found
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
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
Distributed mobility management - framework & analysis
Mobile operators consider the distribution of mobility anchors to enable offloading some traffic from their core network. The Distributed Mobility Management (DMM) Working Group is investigating the impact of decentralized mobility management to existing protocol solutions, while taking into account well defined requirements, which are to be met by a future solution. This document discusses DMM using a functional framework. Functional Entities to support DMM as well as reference points between these Functional Entities are introduced and described. The described functional framework allows distribution and co-location of Functional Entities and build a DMM architecture that matches the architecture of available protocols. Such methodology eases the analysis of best current practices with regard to functional and protocol gaps
an extensible tuplespace as XML-middleware
XMLSpaces.NET implements the Linda concept as a middleware for XML documents.
It introduces an extended matching flexibility on nested tuples and richer
data types for fields, including objects and XML documents. It is completely
XML-based since data, tuples and tuplespaces are seen as trees represented as
XML documents. XMLSpaces.NET is extensible in that it supports a hierarchy of
matching relations on tuples and an open set of matching amongst data,
documents and objects. It is currently being implemented on the .NET platform
High-energy pseudogap in degenerate Hubbard model induced via Hund coupling
Hund coupling in the degenerate five-band Hubbard model near n=6 occupancy is
shown to give rise to a significant depletion of spectral weight above the
Fermi level. Calculations within dynamical mean field theory combined with
exact diagonalization reveal that this pseudogap is associated with a
collective mode in the self-energy caused by spin fluctuations. The pseudogap
is remarkably stable over a wide range of Coulomb and exchange energies, but
disappears for weak Hund coupling. The implications of this phenomenon for
optical spectra of iron pnictides are discussed.Comment: 4 pages, 4 figure
Self-energy and lifetime of Shockley and image states on Cu(100) and Cu(111): Beyond the GW approximation of many-body theory
We report many-body calculations of the self-energy and lifetime of Shockley
and image states on the (100) and (111) surfaces of Cu that go beyond the
approximation of many-body theory. The self-energy is computed in the framework
of the GW\Gamma approximation by including short-range exchange-correlation
(XC) effects both in the screened interaction W (beyond the random-phase
approximation) and in the expansion of the self-energy in terms of W (beyond
the GW approximation). Exchange-correlation effects are described within
time-dependent density-functional theory from the knowledge of an adiabatic
nonlocal XC kernel that goes beyond the local-density approximation.Comment: 8 pages, 5 figures, to appear in Phys. Rev.
Quantum theory of electric polarization nonlinearity in metal nanofilms
We develop a quantum theory of electron confinement in metal nanofilms. The
theory is used to compute the nonlinear response of the film to a static or
low-frequency external electric field and to investigate the role of boundary
conditions imposed on the metal surface. We find that the sign and magnitude of
the nonlinear polarizability depends dramatically on the type of boundary
condition used.Comment: Accepted to PRB in this for
Acoustic surface plasmons in the noble metals Cu, Ag, and Au
We have performed self-consistent calculations of the dynamical response of
the (111) surface of the noble metals Cu, Ag, and Au. Our results indicate that
the partially occupied surface-state band in these materials yields the
existence of acoustic surface plasmons with linear dispersion at small wave
vectors. Here we demonstrate that the sound velocity of these low-energy
collective excitations, which had already been predicted to exist in the case
of Be(0001), is dictated not only by the Fermi velocity of the two-dimensional
surface-state band but also by the nature of the decay and penetration of the
surface-state orbitals into the solid. Our linewidth calculations indicate that
acoustic surface plasmons should be well defined in the energy range from zero
to meV.Comment: 8 pages, two columns, 7 figures, to appear in Phys. Rev.
Phase diagram of orbital-selective Mott transitions at finite temperatures
Mott transitions in the two-orbital Hubbard model with different bandwidths
are investigated at finite temperatures. By means of the self-energy functional
approach, we discuss the stability of the intermediate phase with one orbital
localized and the other itinerant, which is caused by the orbital-selective
Mott transition (OSMT). It is shown that the OSMT realizes two different
coexistence regions at finite temperatures in accordance with the recent
results of Liebsch. We further find that the particularly interesting behavior
emerges around the special condition and J=0, which includes a new type
of the coexistence region with three distinct states. By systematically
changing the Hund coupling, we establish the global phase diagram to elucidate
the key role played by the Hund coupling on the Mott transitions.Comment: 4 pages, 6 figure
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