2,517 research outputs found
Multi-orbital Cluster Perturbation Theory for transition metal oxides
We present an extension of Cluster Perturbation Theory to include many body
correlations associated to local e-e repulsion in real materials. We show that
this approach can describe the physics of complex correlated materials where
different atomic species and different orbitals coexist. The prototypical case
of MnO is considered
Periodically driven interacting electrons in 1D: a many-body Floquet approach
We propose a method to study the time evolution of correlated electrons
driven by an harmonic perturbation. Combining Floquet formalism to include the
time-dependent field and Cluster Perturbation Theory to solve the many-body
problem in the presence of short-range correlations, we treat the electron
double dressing - by photons and by e-e interaction - on the same footing. We
apply the method to an extended Hubbard chain at half occupation and we show
that in the regime of small field frequency and for given values of field
strength the zero-mode Floquet band is no more gapped and the system recovers a
metallic state. Our results are indicative of an omnipresent mechanism for
insulator-to-metal transition in 1D systems
Topological properties of the bond-modulated honeycomb lattice
We study the combined effects of lattice deformation, e-e interaction and
spin-orbit coupling in a two-dimensional (2D) honeycomb lattice. We adopt
different kinds of hopping modulation--generalized dimerization and a Kekule
distortion--and calculate topological invariants for the non-interacting system
and for the interacting system. We identify the parameter range (Hubbard U,
hopping modulation, spin-orbit coupling) where the 2D system behaves as a
trivial insulator or Quantum Spin Hall Insulator.Comment: 8 pages, 4 figures: discussion improved, typos corrected, references
updated. Matches version published in PR
Topological invariants in interacting Quantum Spin Hall: a Cluster Perturbation Theory approach
Using Cluster Perturbation Theory we calculate Green's functions,
quasi-particle energies and topological invariants for interacting electrons on
a 2-D honeycomb lattice, with intrinsic spin-orbit coupling and on-site e-e
interaction. This allows to define the parameter range (Hubbard U vs spin-orbit
coupling) where the 2D system behaves as a trivial insulator or Quantum Spin
Hall insulator. This behavior is confirmed by the existence of gapless
quasi-particle states in honeycomb ribbons. We have discussed the importance of
the cluster symmetry and the effects of the lack of full translation symmetry
typical of CPT and of most Quantum Cluster approaches. Comments on the limits
of applicability of the method are also provided.Comment: 7 pages, 7 figures: discussion improved, one figure added, references
updated. Matches version published in New J. Phy
The associated production of t¯tH in ATLAS
Since its discovery in July 2012, it has become mandatory to study the couplings of the Higgs boson with other Standard Model particles. The associated production of Higgs and top-antitop pairs (t¯tH) gives direct access to the Higgs-top couplings. Due to the different decay modes of the t¯t pairs and of the Higgs boson, the process displays a large variety of decay channels involving in the final state, b¯b pairs, γγ and multileptonic (including τ ) states. Although the sensitivity is still limited by the Run I statistics, the assessment of the analysis methods will be essential for constraining the t-H coupling using the data collected from 2015 at ATLAS at LHC. These include background estimation, selection optimization and
systematics control
Reentrant metallicity in the Hubbard model: the case of honeycomb nanoribbons
Based on the cluster perturbation solution of the Hubbard Hamiltonian for a 2D honeycomb lattice, we present quasi-particle band structures of nanoribbons at half filling as a function of on-site electron-electron (e-e) repulsion. We show that, at moderate values of e-e interaction, ribbons with armchair-shaped edges exhibit an unexpected semimetallic behavior, recovering the original insulating character only at larger values of U
Self-consistent Green function approach for calculations of electronic structure in transition metals
We present an approach for self-consistent calculations of the many-body
Green function in transition metals. The distinguishing feature of our approach
is the use of the one-site approximation and the self-consistent quasiparticle
wave function basis set, obtained from the solution of the Schrodinger equation
with a nonlocal potential. We analyze several sets of skeleton diagrams as
generating functionals for the Green function self-energy, including GW and
fluctuating exchange sets. Their relative contribution to the electronic
structure in 3d-metals was identified. Calculations for Fe and Ni revealed
stronger energy dependence of the effective interaction and self-energy of the
d-electrons near the Fermi level compared to s and p electron states.
Reasonable agreement with experimental results is obtained
Photo-excitation of a light-harvesting supra-molecular triad: a Time-Dependent DFT study
We present the first time-dependent density-functional theory (TDDFT)
calculation on a light harvesting triad carotenoid-diaryl-porphyrin-C60.
Besides the numerical challenge that the ab initio study of the electronic
structure of such a large system presents, we show that TDDFT is able to
provide an accurate description of the excited state properties of the system.
In particular we calculate the photo-absorption spectrum of the supra-molecular
assembly, and we provide an interpretation of the photo-excitation mechanism in
terms of the properties of the component moieties. The spectrum is in good
agreement with experimental data, and provides useful insight on the
photo-induced charge transfer mechanism which characterizes the system.Comment: Accepted for publication on JPC, March 09th 200
First principle theory of correlated transport through nano-junctions
We report the inclusion of electron-electron correlation in the calculation
of transport properties within an ab initio scheme. A key step is the
reformulation of Landauer's approach in terms of an effective transmittance for
the interacting electron system. We apply this framework to analyze the effect
of short range interactions on Pt atomic wires and discuss the coherent and
incoherent correction to the mean-field approach.Comment: 5 pages, 3 figure
- …