312 research outputs found
Electron self-trapping and fluctuation density-of-states tail at the critical point
We consider electron self-trapping due to its interaction with
order-parameter fluuctuations at the second-order phase-transition or critical
point (for example, at the Curie temperature in magnetic or ferroelectric
semiconductors). Using Feynman path integral approach the autolocalization
energy and the size of the self-trapped state (fluctuon) are estimated. It is
shown that the fluctuon states are connected with the Lifshitz tail of the
electron density-of-states, the parameters of this tail being determined by the
critical exponents.Comment: 4 pages, revtex4, Phys. Rev. B, accepte
Ground state of a double-exchange system containing impurities: bounds of ferromagnetism
We study the boundary between ferromagnetic and non-ferromagnetic ground
state of a double-exchange system with quenched disorder for arbitrary relation
between Hund exchange coupling and electron band width. The boundary is found
both from the solution of the Dynamical Mean Field Approximation equations and
from the comparison of the energies of the saturated ferromagnetic and
paramagnetic states. Both methods give very similar results. To explain the
disappearance of ferromagnetism in part of the parameter space we derive from
the double-exchange Hamiltonian with classical localized spins in the limit of
large but finite Hund exchange coupling the model (with classical
localized spins).Comment: 5 pages, 8 eps figures, latex; minor typos correcte
Long-time asymptotic of temporal-spatial coherence function for light propagation through time dependent disorder
Long-time asymptotic of field-field correlator for radiation propagated
through a medium composed of random point-like scatterers is studied using
Bete-Salpeter equation. It is shown that for plane source the fluctuation
intensity (zero spatial moment of the correlator) obeys a power-logarithmic
stretched exponential decay law, the exponent and preexponent being dependent
on the scattering angle. Spatial center of gravity and dispersion of the
correlator (normalized first and second spatial moments, respectively) prove to
weakly diverge as time tends to infinity. A spin analogy of this problem is
discussed.Comment: 12 pages, Latex, no figures, to be publication in Phys. Lett.
Non-quasiparticle states in the core level spectra of ferromagnetic semiconductors and half-metallic ferromagnets
The Green's functions that determine x-ray spectra are calculated in the s-d
exchange model of a saturated conducting ferromagnet in the presence of the
core hole. A possibility to observe non-quasiparticle (NQP) states in the core
level (x-ray absorption, emission and photoelectron) spectroscopy is
demonstrated. It is shown that NQP contributions to resonant x-ray scattering
spectra can be considerably enhanced by core hole effects in comparison with
those to the density of states.Comment: 13 pages, 7 figures, final versio
Spin-polarized scanning tunneling microscopy of half-metallic ferromagnets: Non-quasiparticle contributions
The role of the many-body (spin-polaronic) effects in the scanning tunneling
spectroscopy of half-metallic ferromagnets (HMF) is considered. It is shown
that the non-quasiparticle (NQP) states exist in the majority or minority spin
gap in the presence of arbitrary external potential and, in particular, at the
surfaces and interfaces. Energy dependence of the NQP density of states is
obtained in various models of HMF, an important role of the hybridization
nature of the energy gap being demonstrated. The corresponding temperature
dependence of spin polarization is calculated. It is shown that the NQP states
result in a sharp bias dependence of the tunneling conductance near zero bias.
Asymmetry of the NQP states with respect to the Fermi energy provides an
opportunity to separate phonon and magnon peaks in the inelastic spectroscopy
by STM.Comment: 13 pages, 6 figure
Ferromagnetic transition in a double-exchange system containing impurities in the Dynamical Mean Field Approximation
We formulate the Dynamical Mean Field Approximation equations for the
double-exchange system with quenched disorder for arbitrary relation between
Hund exchange coupling and electron band width. Close to the
ferromagnetic-paramagnetic transition point the DMFA equations can be reduced
to the ordinary mean field equation of Curie-Weiss type. We solve the equation
to find the transition temperature and present the magnetic phase diagram of
the system.Comment: 5 pages, latex, 2 eps figures. We explicitely present the magnetic
phase diagram of the syste
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