2,498 research outputs found
Correlation effects in electronic structure of PuCoGa5
We report on results of the first realistic electronic structure calculations
of the Pu-based PuCoGa5 superconductor based on the dynamical mean field
theory. We find that dynamical correlations due to the local Coulomb
interaction between Pu f-electrons lead to substantial modification of the
electronic structure with a narrow peak being formed in vicinity of the Fermi
energy, in agreement with the experimental photoemission spectra, and in
contrast with the recent calculations within the LDA+U method, where only
static electronic correlations have been included. Both Pu and Co contribute in
equal footing to the narrow peak on the density of states at the Fermi level,
the Co partial density of states being prominently affected by electronic
correlations on the Pu sites. The k-resolved spectral density is calculated and
the theoretical spectral function resolved extended Van Hove singularity near
the Fermi energy. This singularity may lead to enchancement of the magnetic
susceptebility and favour d-wave superconductivity
On evolutionary origin of cancer
BACKGROUND: The necessary and sufficient capabilities of cancer cell have been identified. Strikingly, this list does not include one that would seem to be a key property, namely the ability of cancer cells to kill their "host". This is believed to be a self-evident consequence of the other capabilities (e.g., metastasis), although the available evidence suggests a distinct killer function. Taking into account this unlisted property can significantly affect the current paradigm of carcinogenesis. PRESENTATION OF THE HYPOTHESIS: On the assumption that killer function is a key capability of the cancer cell, it is suggested that cancer has evolved as a mechanism of negative selection of mutant alleles of vitally important genes present in population. Similarly to apoptosis, which is an altruistic suicidal act of a damaged cell, cancer is an altruistic suicidal act of an individual who carries dangerous alleles and presents a hazard for genetic stability of the population. From this point of view, apoptosis is not a protection means against cancer as generally believed, but rather they are the first and second lines of defense against genome instability, respectively. TESTING THE HYPOTHESIS: The modern DNA array technology is capable of revealing gene expression profiles responsible for killer function of cancer cell as well as those specific targets in the body that are most strongly affected by the tumor growth. IMPLICATIONS OF THE HYPOTHESIS: This hypothesis suggests new avenues of cancer research as well as principally new therapeutic strategies
Electronic correlations and competing orders in multiorbital dimers: a cluster DMFT study
We investigate the violation of the first Hund's rule in 4 and 5
transition metal oxides that form solids of dimers. Bonding states within these
dimers reduce the magnetization of such materials. We parametrize the dimer
formation with realistic hopping parameters and find not only regimes, where
the system behaves as a Fermi liquid or as a Peierls insulator, but also
strongly correlated regions due to Hund's coupling and its competition with the
dimer formation. The electronic structure is investigated using the cluster
dynamical mean-field theory for a dimer in the two-plane Bethe lattice with two
orbitals per site and -filling, that is three electrons per dimer. It
reveals dimer-antiferromagnetic order of a high-spin (double exchange) state
and a low-spin (molecular orbital) state. At the crossover region we observe
the suppression of long-range magnetic order, fluctuation enhancement and
renormalization of electron masses. At certain interaction strengths the system
becomes an incoherent antiferromagnetic metal with well defined local moments.Comment: 11 pages, 10 figure
Correlated band theory of spin and orbital contributions to Dzyaloshinskii-Moriya interactions
A new approach for calculations of Dzyaloshinskii-Moriya interactions in
molecules and crystals is proposed. It is based on the exact perturbation
expansion of total energy of weak ferromagnets in the canting angle with the
only assumption of local Hubbard-type interactions. This scheme leads to a
simple and transparent analytical expression for Dzyaloshinskii-Moriya vector
with a natural separation into spin and orbital contributions. The main problem
was transferred to calculations of effective tight-binding parameters in the
properly chosen basis including spin-orbit coupling. Test calculations for
LaCuO give the value of canting angle in a good agreement with
experimental data.Comment: 4 pages, 1 figur
Correlated adatom trimer on metal surface: A continuous time quantum Monte Carlo study
The problem of three interacting Kondo impurities is solved within a
numerically exact continuous time quantum Monte Carlo scheme. A suppression of
the Kondo resonance by interatomic exchange interactions for different cluster
geometries is investigated. It is shown that a drastic difference between the
Heisenberg and Ising cases appears for antiferromagnetically coupled adatoms.
The effects of magnetic frustrations in the adatom trimer are investigated, and
possible connections with available experimental data are discussed.Comment: 4 pages, 4 figure
Local impurity effects in superconducting graphene
We study the effect of impurities in superconducting graphene and discuss
their influence on the local electronic properties. In particular, we consider
the case of magnetic and non-magnetic impurities being either strongly
localized or acting as a potential averaged over one unit cell. The spin
dependent local density of states is calculated and possibilities for
visualizing impurities by means of scanning tunneling experiments is pointed
out. A possibility of identifying magnetic scatters even by non spin-polarized
scanning tunneling spectroscopy is explained.Comment: 4 pages, 4 figure
Exact diagonalization solver for the extended dynamical mean-field theory
We present an efficient exact diagonalization scheme for the extended
dynamical mean-field theory and apply it to the extended Hubbard model on the
square lattice with nonlocal charge-charge interactions. Our solver reproduces
the phase diagram of this approximation with good accuracy. Details on the
numerical treatment of the large Hilbert space of the auxiliary
Holstein-Anderson impurity problem are provided. Benchmarks with a numerically
exact strong-coupling continuous-time quantum-Monte Carlo solver show better
convergence behavior of the exact diagonalization in the deep insulator.
Special attention is given to possible effects due to the discretization of the
bosonic bath. We discuss the quality of real axis spectra and address the
question of screening in the Mott insulator within extended dynamical
mean-field theory.Comment: 12 pages, 8 figure
Renormalized spectral function for Co adatom on the Pt(111) surface
The strong Coulomb correlations effects in the electronic structure of
magnetic Co adatom on the Pt(111) surface have been investigated. Using a
realistic five d-orbital impurity Anderson model at low temperatures with
parameters determined from first-principles calculations we found a striking
change of the electronic structure in comparison with the LDA results. The
spectral function calculated with full rotationally invariant Coulomb
interaction is in good agreement with the quasiparticle region of the STM
conductance spectrum. Using the calculated spin-spin correlation functions we
have analyzed the formation of the magnetic moments of the Co impurity
orbitals.Comment: 4 pages, 4 figure
Continuous Time Quantum Monte Carlo method for fermions
We present numerically exact continuous-time Quantum Monte Carlo algorithm
for fermions with a general non-local in space-time interaction. The new
determinantal grand-canonical scheme is based on a stochastic series expansion
for the partition function in the interaction representation. The method is
particularly applicable for multi-band time-dependent correlations since it
does not invoke the Hubbard-Stratonovich transformation. The test calculations
for exactly solvable models as well results for the Green function and for the
time-dependent susceptibility of the multi-band super-symmetric model with a
spin-flip interaction are discussed.Comment: 10 pages, 7 Figure
Hydrogen on graphene: Electronic structure, total energy, structural distortions, and magnetism from first-principles calculations
Density functional calculations of electronic structure, total energy,
structural distortions, and magnetism for hydrogenated single-layer, bilayer,
and multi-layer graphene are performed. It is found that hydrogen-induced
magnetism can survives only at very low concentrations of hydrogen (single-atom
regime) whereas hydrogen pairs with optimized structure are usually
nonmagnetic. Chemisorption energy as a function of hydrogen concentration is
calculated, as well as energy barriers for hydrogen binding and release. The
results confirm that graphene can be perspective material for hydrogen storage.
Difference between hydrogenation of graphene, nanotubes, and bulk graphite is
discussed.Comment: 8 pages 8 figures (accepted to Phys. Rev. B
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