77 research outputs found
Quantum self-induced transparency in frequency gap media
We study quantum effects of light propagation through an extended absorbing
system of two-level atoms placed within a frequency gap medium (FGM). Apart
from ordinary solitons and single particle impurity band states, the
many-particle spectrum of the system contains massive pairs of confined gap
excitations and their bound complexes - gap solitons. In addition,
``composite'' solitons are predicted as bound states of ordinary and gap
solitons. Quantum gap and composite solitons propagate without dissipation, and
should be associated with self-induced transparency pulses in a FGM.Comment: 5 pages, RevTe
Ground State Properties of Anderson Impurity in a Gapless Host
Using the Bethe ansatz method, we study the ground state properties of a
Anderson impurity in a ``gapless'' host, where a density of band
states vanishes at the Fermi level as . As
in metals, the impurity spin is proven to be screened at arbitrary parameters
of the system. However, the impurity occupancy as a function of the bare
impurity energy is shown to acquire novel qualitative features which
demonstrate a nonuniversal behavior of the system. The latter explains why the
Kondo screening is absent (or exists only at quite a large electron-impurity
coupling) in earlier studies based on scaling arguments.Comment: 5 pages, no figure, RevTe
Multiphoton localization and propagating quantum gap solitons in a frequency gap medium
The many-particle spectrum of an isotropic frequency gap medium doped with
impurity resonance atoms is studied using the Bethe ansatz technique. The
spectrum is shown to contain pairs of quantum correlated ``gap excitations''
and their heavy bound complexes (``gap solitons''), enabling the propagation of
quantum information within the classically forbidden gap. In addition,
multiparticle localization of the radiation and the medium polarization occurs
when such a gap soliton is pinned to the impurity atom.Comment: 8 pages, RevTEX, to appear in Phys. Rev. Let
Bethe ansatz approach to thermodynamics of superconducting magnetic alloys
We derive thermodynamic Bethe ansatz equations for a model describing an
Anderson impurity embedded in a BCS superconductor. The equations
are solved analytically in the zero-temperature limit, T=0. It is shown that
the impurities depress superconductivity in the Kondo limit, however at T=0 the
system remains in the superconducting state for any impurity concentration. In
the mixed-valence regime, an impurity contribution to the density of states of
the system near the Fermi level overcompensates a Cooper pairs weakening, and
superconductivity is enhanced.Comment: 4 pages, RevTex, to appear in PR
Exactly solvable toy models of unconventional magnetic alloys: Bethe Ansatz versus Renormalization Group method
We propose toy models of unconventional magnetic alloys, in which the density
of band states, , and hybridization, , are energy
dependent; it is assumed, however, that
, and hence an effective
electron-impurity coupling is
energy independent. In the renormalization group approach, the physics of the
system is assumed to be governed by only rather than by
separate forms of and . However, an exact Bethe
Ansatz solution of the toy Anderson model demonstrates a crucial role of a form
of inverse band dispersion .Comment: A final version. A previous one has been sent to Archive because of
my technical mistake. Sorr
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Oxygen diffusion in Sr<sub>0.75</sub>Y<sub>0.25</sub>CoO<sub>2.625</sub>: a molecular dynamics study
Oxygen diffusion in Sr0.75Y0.25CoO2.625 is investigated using molecular dynamics simulations in conjunction with an established set of Born model potentials. We predict an activation energy of diffusion for 1.56 eV in the temperature range of 1000-1400 K. We observe extensive disordering of the oxygen ions over a subset of lattice sites. Furthermore, oxygen ion diffusion both in the a-b plane and along the c axis requires the same set of rate-limiting ion hops. It is predicted that oxygen transport in Sr0.75Y0.25CoO2.625 is therefore isotropic
Scattering of massless particles in one-dimensional chiral channel
We present a general formalism describing a propagation of an arbitrary
multiparticle wave packet in a one-dimensional multimode chiral channel coupled
to an ensemble of emitters which are distributed at arbitrary positions. The
formalism is based on a direct and exact resummation of diagrammatic series for
the multiparticle scattering matrix. It is complimentary to the Bethe Ansatz
and to approaches based on equations of motion, and it reveals a simple and
transparent structure of scattering states. In particular, we demonstrate how
this formalism works on various examples, including scattering of one- and
two-photon states off two- and three-level emitters, off an array of emitters
as well as scattering of coherent light. We argue that this formalism can be
constructively used for study of scattering of an arbitrary initial photonic
state off emitters with arbitrary degree of complexity.Comment: 25 pages, 5 figure
Effects of resonant tunneling in electromagnetic wave propagation through a polariton gap
We consider tunneling of electromagnetic waves through a polariton band gap
of a 1-D chain of atoms. We analytically show that a defect embedded in the
structure gives rise to the resonance transmission at the frequency of a local
polariton state associated with the defect. Numerical Monte-Carlo simulations
are used to examine properties of the electromagnetic band arising inside the
polariton gap due to finite concentration of defects.Comment: 12 pages, 6 figures, RevTe
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