14,133 research outputs found
Oblique amplitude modulation of dust-acoustic plasma waves
Theoretical and numerical studies are presented of the nonlinear amplitude
modulation of dust-acoustic (DA) waves propagating in an unmagnetized three
component, weakly-coupled, fully ionized plasma consisting of electrons,
positive ions and charged dust particles, considering perturbations oblique to
the carrier wave propagation direction. The stability analysis, based on a
nonlinear Schroedinger-type equation (NLSE), shows that the wave may become
unstable; the stability criteria depend on the angle between the
modulation and propagation directions. Explicit expressions for the instability
rate and threshold have been obtained in terms of the dispersion laws of the
system. The possibility and conditions for the existence of different types of
localized excitations have also been discussed.Comment: 21 pages, 6 figures, to appear in Physica Script
On the characterisation of paired monotone metrics
Hasegawa and Petz introduced the notion of dual statistically monotone
metrics. They also gave a characterisation theorem showing that
Wigner-Yanase-Dyson metrics are the only members of the dual family. In this
paper we show that the characterisation theorem holds true under more general
hypotheses.Comment: 12 pages, to appear on Ann. Inst. Stat. Math.; v2: changes made to
conform to accepted version, title changed as wel
Stable embedded solitons
Stable embedded solitons are discovered in the generalized third-order
nonlinear Schroedinger equation. When this equation can be reduced to a
perturbed complex modified KdV equation, we developed a soliton perturbation
theory which shows that a continuous family of sech-shaped embedded solitons
exist and are nonlinearly stable. These analytical results are confirmed by our
numerical simulations. These results establish that, contrary to previous
beliefs, embedded solitons can be robust despite being in resonance with the
linear spectrum.Comment: 2 figures. To appear in Phys. Rev. Let
Decoherence modes of entangled qubits within neutron interferometry
We study two different decoherence modes for entangled qubits by considering
a Liouville - von Neumann master equation. Mode A is determined by projection
operators onto the eigenstates of the Hamiltonian and mode B by projectors onto
rotated states. We present solutions for general and for Bell diagonal states
and calculate for the later the mixedness and the amount of entanglement given
by the concurrence.
We propose a realization of the decoherence modes within neutron
interferometry by applying fluctuating magnetic fields. An experimental test of
the Kraus operator decomposition describing the evolution of the system for
each mode is presented.Comment: 15 pages, 5 figure
Optical Solitary Waves in the Higher Order Nonlinear Schrodinger Equation
We study solitary wave solutions of the higher order nonlinear Schrodinger
equation for the propagation of short light pulses in an optical fiber. Using a
scaling transformation we reduce the equation to a two-parameter canonical
form. Solitary wave (1-soliton) solutions exist provided easily met inequality
constraints on the parameters in the equation are satisfied. Conditions for the
existence of N-soliton solutions (N>1) are determined; when these conditions
are met the equation becomes the modified KdV equation. A proper subset of
these conditions meet the Painleve plausibility conditions for integrability.Comment: REVTeX, 4 pages, no figures. To appear in Phys. Rev. Let
Slave-Boson Mean-Field Theory of the Antiferromagnetic State in the Doubly Degenerate Hubbard Model - the Half-Filled Case -
The antiferromagnetic ground state of the half-filled Hubbard model with the
doubly degenerate orbital has been studied by using the slave-boson mean-field
theory which was previously proposed by the present author. Numerical
calculations for the simple cubic model have shown that the metal-insulator
transition does not take place except at the vanishing interaction point, in
strong contrast with its paramagnetic solution. The energy gap in the density
of states of the antiferromagnetic insulator is much reduced by the effect of
electron correlation. The exchange interaction plays an important role in
the antiferromagnetism: although for the sublattice magnetic moment
in our theory is fairly smaller than obtained in the Hartree-Fock
approximation, for (: the Coulomb interaction) is increased
to become comparable to . Surprisingly, the antiferromagnetic state is
easily destroyed if a small, negative exchange interaction () is
introduced.Comment: Latex 18 pages, 12 figures available on request to
[email protected] Note: published in Phys. Rev. B with some minor
modification
Photogenerated Carriers in SrTiO3 Probed by Mid-Infrared Absorption
Infrared absorption spectra of SrTiO have been measured under
above-band-gap photoexcitations to study the properties of photogenerated
carriers, which should play important roles in previously reported photoinduced
phenomena in SrTiO. A broad absorption band appears over the entire
mid-infrared region under photoexcitation. Detailed energy, temperature, and
excitation power dependences of the photoinduced absorption are reported. This
photo-induced absorption is attributed to the intragap excitations of the
photogenerated carriers. The data show the existence of a high density of
in-gap states for the photocarriers, which extends over a wide energy range
starting from the conduction and valence band edges.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp
Superconductivity of Quasi-One and Quasi-Two Dimensional Tight-Binding Electrons in Magnetic Field
The upper critical field of the tight-binding electrons in the
three-dimensional lattice is investigated.
The electrons make Cooper pairs between the eigenstates with the same energy
in the strong magnetic field. The transition lines in the quasi-one dimensional
case are shown to deviate from the previously obtained results where the
hopping matrix elements along the magnetic field are neglected. In the absence
of the Pauli pair breaking the transition temperature of the quasi-two
dimensional electrons is obtained to oscillationally increase as the magnetic
field becomes large and reaches to in the strong field as in the
quasi-one dimensional case.Comment: 4pages,4figures,to be published in J.Phys.Soc.Jp
The Metal-Insulator Transition in the Doubly Degenerate Hubbard Model
A systematic study has been made on the metal-insulator (MI) transition of
the doubly degenerate Hubbard model (DHM) in the paramagnetic ground state, by
using the slave-boson mean-field theory which is equivalent to the Gutzwiller
approximation (GA). For the case of infinite electron-electron interactions, we
obtain the analytic solution, which becomes exact in the limit of infinite
spatial dimension. On the contrary, the finite-interaction case is investigated
by numerical methods with the use of the simple-cubic model with the
nearest-neighbor hopping. The mass-enhancement factor, , is shown to
increase divergently as one approaches the integer fillings (), at
which the MI transition takes place, being the total number of electrons.
The calculated dependence of is compared with the observed
specific-heat coefficient, , of which is reported
to significantly increase as approaches unity.Comment: Latex 16 pages, 10 ps figures included, published in J. Phys. Soc.
Jpn. with some minor modifications. ([email protected]
Fluctuation Conductivity in Unconventional Superconductors near Critical Disorder
The fluctuation conductivity in bulk superconductors with
non s-wave pairing and with nonmagnetic disorder of strength is studied at
low and within the Gaussian approximation. It is shown by assuming a quasi
two-dimensional (2D) electronic state that, only if the gap function
d_\mu({\p}) is, as in a 2D p-wave pairing state, linear in the in-plane
(relative) momentum {\p}_\perp, the in-plane fluctuation conductivity on the
line is weakly divergent in low limit. The present result may be
useful in clarifying the true gap function of spin-triplet
through resistivity measurements.Comment: 8 pages, 1 figure, to be published in J. Phys. Soc. Jpn. 70, No.10
(2001
- …