55,477 research outputs found
Casimir stress in an inhomogeneous medium
The Casimir effect in an inhomogeneous dielectric is investigated using
Lifshitz's theory of electromagnetic vacuum energy. A permittivity function
that depends continuously on one Cartesian coordinate is chosen, bounded on
each side by homogeneous dielectrics. The result for the Casimir stress is
infinite everywhere inside the inhomogeneous region, a divergence that does not
occur for piece-wise homogeneous dielectrics with planar boundaries. A Casimir
force per unit volume can be extracted from the infinite stress but it diverges
on the boundaries between the inhomogeneous medium and the homogeneous
dielectrics. An alternative regularization of the vacuum stress is considered
that removes the contribution of the inhomogeneity over small distances, where
macroscopic electromagnetism is invalid. The alternative regularization yields
a finite Casimir stress inside the inhomogeneous region, but the stress and
force per unit volume diverge on the boundaries with the homogeneous
dielectrics. The case of inhomogeneous dielectrics with planar boundaries thus
falls outside the current understanding of the Casimir effect.Comment: 17 page
Effect of high-K dielectrics on charge transport in graphene
The effect of various dielectrics on charge mobility in single layer graphene
is investigated. By calculating the remote optical phonon scattering arising
from the polar substrates, and combining it with their effect on Coulombic
impurity scattering, a comprehensive picture of the effect of dielectrics on
charge transport in graphene emerges. It is found that though high-
dielectrics can strongly reduce Coulombic scattering by dielectric screening,
scattering from surface phonon modes arising from them wash out this advantage.
By comparing the room-temperature transport properties with narrow-bandgap
III-V semiconductors, strategies to improve the mobility in single layer
graphene are outlined.Comment: 6 pages, 4 Figure
Measured current drainage through holes in various dielectrics up to 2 kilovolts in a dilute plasma
The electron current drained from a plasma through approximately 0.05 cm diameter holes in eight possible space applicable dielectrics placed on a probe biased at voltages up to 2000 V dc have been determined both theoretically and experimentally. The dielectrics tested were Parylene C and N, Teflon FEP type C, Teflon TFE, Nomex, quartz 7940 Corning Glass, Mylar A, and Kapton H polymide film. A Laplace field was used to predict an upper limit for the drainage current. The measured current was less than the computed current for quartz, Teflon FEP, and the 0.0123 cm thick sample of Parylene N for all voltages tested. The drainage current through the other dielectrics became equal to or greater than the computed current at a voltage below 2000 V. The magnitudes of the currents were between 0.1 and 10 microamperes for most of the dielectrics
The issue of photons in dielectrics: Hamiltonian viewpoint
The definition of the photon in the vacuum of general relativity provided by
Kermack et al. and by Synge is extended to nondispersive, nonhomogeneous,
isotropic dielectrics in arbitrary motion by Hamiltonian methods that rely on
Gordon's effective metric. By these methods the old dilemma, whether the
momentum-energy vector of the photon in dielectrics is timelike or spacelike in
character, is shown to reappear under a novel guise.Comment: 12 pages, one figure; text to appear in Nuovo Cimento
The issue of photons in dielectrics: Hamiltonian viewpoint
The definition of the photon in the vacuum of general relativity provided by
Kermack et al. and by Synge is extended to nondispersive, nonhomogeneous,
isotropic dielectrics in arbitrary motion by Hamiltonian methods that rely on
Gordon's effective metric. By these methods the old dilemma, whether the
momentum-energy vector of the photon in dielectrics is timelike or spacelike in
character, is shown to reappear under a novel guise.Comment: 12 pages, one figure; text to appear in Nuovo Cimento
Nonlinear graphene plasmonics: amplitude equation
Using perturbation expansion of Maxwell equations, the amplitude equation is
derived for nonlinear TM and TE surface plasmon waves supported by graphene.
The equation describes interplay between in-plane beam diffraction and
nonlinerity due to light intensity induced corrections to graphene conductivity
and susceptibility of dielectrics. For strongly localized TM plasmons, graphene
is found to bring the superior contribution to the overall nonlinearity. In
contrast, nonlinear response of the substrate and cladding dielectrics can
become dominant for weakly localized TE plasmons.Comment: published in Phys. Rev.
Thermal quantum field theory and the Casimir interaction between dielectrics
The Casimir and van der Waals interaction between two dissimilar thick
dielectric plates is reconsidered on the basis of thermal quantum field theory
in Matsubara formulation. We briefly review two main derivations of the
Lifshitz formula in the framework of thermal quantum field theory without use
of the fluctuation-dissipation theorem. A set of special conditions is
formulated under which these derivations remain valid in the presence of
dissipation. The low-temperature behavior of the Casimir and van der Waals
interactions between dissimilar dielectrics is found analytically from the
Lifshitz theory for both an idealized model of dilute dielectrics and for real
dielectrics with finite static dielectric permittivities. The free energy,
pressure and entropy of the Casimir and van der Waals interactions at low
temperatures demonstrate the same universal dependence on the temperature as
was previously discovered for ideal metals. The entropy vanishes when
temperature goes to zero proving the validity of the Nernst heat theorem. This
solves the long-standing problem on the consistency of the Lifshitz theory with
thermodynamics in the case of dielectric plates. The obtained asymptotic
expressions are compared with numerical computations for both dissimilar and
similar real dielectrics and found to be in excellent agreement. The role of
the zero-frequency term in Matsubara sum is investigated in the case of
dielectric plates. It is shown that the inclusion of conductivity in the model
of dielectric response leads to the violation of the Nernst heat theorem. The
applications of this result to the topical problems of noncontact atomic
friction and the Casimir interaction between real metals are discussed.Comment: 39 pages, 4 figures, to appear in Phys. Rev.
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