926 research outputs found
Spin and orbital ferromagnetism in strongly correlated itinerant electron systems
Spectra of one-electron and collective excitations in narrow-band
ferromagnets with unquenched orbital moments are calculated in various
theoretical models. The interaction of spin and orbital excitations with
conduction electrons results in the damping of the former which, however, turns
out to be rather small; therefore, apart from usual spin waves, well-defined
orbitons can exist. Non-quasiparticle states occur in the electron energy
spectrum near the Fermi energy due to this interaction. The criteria of
stability of the saturated spin and orbital ferromagnetic ordering are
considered. Possible effects of orbital ordering in magnetite and in colossal
magnetoresistance manganites are discussed.Comment: 12 pages, 4 figures, Revtex, PRB, accepte
Spin relaxation related to the edge scattering in graphene
We discuss the role of spin-flip scattering of electrons from the magnetized
edges in graphene nanoribbons. The spin-flip scattering is associated with
strong fluctuations of the magnetic moments at the edge. Using the Boltzmann
equation approach, which is valid for not too narrow nanoribbons, we calculate
the spin relaxation time in the case of Berry-Mondragon and zigzag graphene
edges. We also consider the case of ballistic nanoribbons characterized by very
long momentum relaxation time in the bulk, when the main source of momentum and
spin relaxation is the spin-dependent scattering at the edges. We found that in
the case of zigzag edges, an anomalous spin diffusion is possible, which is
related to very weak spin-flip scattering of electrons gliding along the
nanoribbon edge.Comment: 9 pages, 7 figure
Nonperturbative anharmonic phenomena in crystal lattice dynamics
Slow dynamics of energy transfer between different phonon modes under the
resonance conditions is considered. It may result in new effects in the
inelastic and quasielastic neutron scattering spectra.Comment: Contribution to the proceedings of the 3rd International Symposium on
Slow Dynamics in Complex Systems (Sendai, Japan,November 3-8, 2003), to be
published in AIP Conference series, 200
Magnetism and interaction-induced gap opening in graphene with vacancies or hydrogen adatoms: Quantum Monte Carlo study
We study electronic properties of graphene with finite concentration of
vacancies or other resonant scatterers by a straightforward lattice Quantum
Monte Carlo calculations. Taking into account realistic long-range Coulomb
interaction we calculate distribution of spin density associated to midgap
states and demonstrate antiferromagnetic ordering. Energy gaps are open due to
the interaction effects, both in the bare graphene spectrum and in the
vacancy/impurity bands. In the case of 5 % concentration of resonant scatterers
the latter gap is estimated as 0.7 eV and 1.1 eV for graphene on boron nitride
and freely suspended graphene, respectively.Comment: Text is substantially updated, temperature dependence of order
parameter is added. Accepted for publication in PR
An dynamical-mean-field-theory investigation of specific heat and electronic structure of and -plutonium
We have carried out a comparative study of the electronic specific heat and
electronic structure of and -plutonium using dynmical mean
field theory (DMFT). We use the perturbative T-matrix and fluctuating exchange
(T-matrix FLEX) as a quantum impurity solver. We considered two different
physical pictures of plutonoium. In the first, , the perturbative
treatment of electronic correlations has been carried out around the
non-magnetic (LDA) Hamiltonian, which results in an f occupation around a bit
above . In the second, , plutonium is viewed as being close
to an configuration, and perturbation theory is carried out around the
(LDA+U) starting point bit below . In the latter case the electronic
specific heat coefficient attains a smaller value in -Pu than
in -Pu, in contradiction to experiment, while in the former case our
calculations reproduce the experimentally observed large increase of
in -Pu as compared to the phase. This enhancement of the
electronic specific heat coefficient in -Pu is due to strong electronic
correlations present in this phase, which cause a substantial increase of the
electronic effective mass, and high density of states at . The densities
of states of and -plutonium obtained starting from the
open-shell configuration are also in good agreement with the experimental
photoemission spectra.Comment: 6 pages, 3 figure
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