4,512 research outputs found
Asymptotic pointwise behavior for systems of semilinear wave equations in three space dimensions
In connection with the weak null condition, Alinhac introduced a sufficient
condition for global existence of small amplitude solutions to systems of
semilinear wave equations in three space dimensions. We introduce a slightly
weaker sufficient condition for the small data global existence, and we
investigate the asymptotic pointwise behavior of global solutions for systems
satisfying this condition. As an application, the asymptotic behavior of global
solutions under the Alinhac condition is also derived.Comment: 56 pages, the final versio
Raman Scattering Spectra of Elementary Electronic Excitations in Coupled Double-Quantum Well Structures
Using the time-dependent-local-density-approximation (TDLDA) within a
self-consistent linear response theory, we calculate the elementary excitation
energies and the associated inelastic light-scattering spectra of a strongly
coupled two-component plasma in a double-quantum well system with electron
occupation of symmetric and antisymmetric subbands. We find, consistent with
the results of a recent experimental Raman scattering study, that the
intersubband spin density excitations tend to merge with the single particle
excitations (i.e. the excitonic shift decreases monotonically) as the Fermi
energy increases beyond the symmetric-antisymmetric energy gap
. However, our TDLDA calculation does not show the abrupt
suppresion of the excitonic shift seen experimentally at a finite value of the
subband occupancy parameter .Comment: 9 pages, RevTeX, 5 figures available upon request, PIT-SDS-00
Investigation of the spin-glass regime between the antiferromagnetic and superconducting phases in FeSeTe
Using bulk magnetization along with elastic and inelastic neutron scattering
techniques, we have investigated the phase diagram of
FeSeTe and the nature of magnetic correlations in three
nonsuperconducting samples of FeSeTe,
FeSeTe and FeSeTe. A cusp
and hysteresis in the temperature dependence of the magnetization for the
and 0.3 samples indicates spin-glass (SG) ordering below K. Neutron scattering measurements indicate that the spin-glass behavior is
associated with short-range spin density wave (SDW) ordering characterized by a
static component and a low-energy dynamic component with a characteristic
incommensurate wave vector of and an anisotropy
gap of 2.5 meV. Our high -resolution data also show that the
systems undergo a glassy structural distortion that coincides with the
short-range SDW order
Global existence for coupled systems of nonlinear wave and Klein-Gordon equations in three space dimensions
We consider the Cauchy problem for coupled systems of wave and Klein-Gordon
equations with quadratic nonlinearity in three space dimensions. We show global
existence of small amplitude solutions under certain condition including the
null condition on self-interactions between wave equations. Our condition is
much weaker than the strong null condition introduced by Georgiev for this kind
of coupled system. Consequently our result is applicable to certain physical
systems, such as the Dirac-Klein-Gordon equations, the Dirac-Proca equations,
and the Klein-Gordon-Zakharov equations.Comment: 31 pages. The final versio
Coupling of spin and orbital excitations in the iron-based superconductor FeSe(0.5)Te(0.5)
We present a combined analysis of neutron scattering and photoemission
measurements on superconducting FeSe(0.5)Te(0.5). The low-energy magnetic
excitations disperse only in the direction transverse to the characteristic
wave vector (1/2,0,0), whereas the electronic Fermi surface near (1/2,0,0)
appears to consist of four incommensurate pockets. While the spin resonance
occurs at an incommensurate wave vector compatible with nesting, neither
spin-wave nor Fermi-surface-nesting models can describe the magnetic
dispersion. We propose that a coupling of spin and orbital correlations is key
to explaining this behavior. If correct, it follows that these nematic
fluctuations are involved in the resonance and could be relevant to the pairing
mechanism.Comment: 4 pages, 4 figures; accepted versio
Correlation induced phonon softening in low density coupled bilayer systems
We predict a possible phonon softening instability in strongly correlated
coupled semiconductor bilayer systems. By studying the plasmon-phonon coupling
in coupled bilayer structures, we find that the renormalized acoustic phonon
frequency may be softened at a finite wave vector due to many-body local field
corrections, particularly in low density systems where correlation effects are
strong. We discuss experimental possibilities to search for this predicted
phonon softening phenomenon.Comment: 4 pages with 2 figure
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