1,941 research outputs found
Casimir effect with rough metallic mirrors
We calculate the second order roughness correction to the Casimir energy for
two parallel metallic mirrors. Our results may also be applied to the
plane-sphere geometry used in most experiments. The metallic mirrors are
described by the plasma model, with arbitrary values for the plasma wavelength,
the mirror separation and the roughness correlation length, with the roughness
amplitude remaining the smallest length scale for perturbation theory to hold.
From the analysis of the intracavity field fluctuations, we obtain the
Casimir energy correction in terms of generalized reflection operators, which
account for diffraction and polarization coupling in the scattering by the
rough surfaces. We present simple analytical expressions for several limiting
cases, as well as numerical results that allow for a reliable calculation of
the roughness correction in real experiments. The correction is larger than the
result of the Proximity Force Approximation, which is obtained from our theory
as a limiting case (very smooth surfaces).Comment: 16 page
Lateral Casimir-Polder force with corrugated surfaces
We derive the lateral Casimir-Polder force on a ground state atom on top of a
corrugated surface, up to first order in the corrugation amplitude. Our
calculation is based on the scattering approach, which takes into account
nonspecular reflections and polarization mixing for electromagnetic quantum
fluctuations impinging on real materials. We compare our first order exact
result with two commonly used approximation methods. We show that the proximity
force approximation (large corrugation wavelengths) overestimates the lateral
force, while the pairwise summation approach underestimates it due to the
non-additivity of dispersion forces. We argue that a frequency shift
measurement for the dipolar lateral oscillations of cold atoms could provide a
striking demonstration of nontrivial geometrical effects on the quantum vacuum.Comment: 12 pages, 6 figures, contribution to QFEXT07 proceeding
Influence of slab thickness on the Casimir force
We calculate the Casimir force between slabs of finite thickness made of
intrinsic and doped silicon with different concentration of carriers and
compare the results to those obtained for gold slabs. We use the Drude and the
plasma models to describe the dielectric function for the carriers in doped Si.
We discuss the possibility of experimentally testing the appropriateness of
these models. We also investigate the influence of finite thickness on ,
which has recently been proposed for Casimir effect measurements testing the
metal-insulator transition.Comment: 10 pages, 10 figures, 2 tables, v2, typos correcte
Casimir energy and geometry : beyond the Proximity Force Approximation
We review the relation between Casimir effect and geometry, emphasizing
deviations from the commonly used Proximity Force Approximation (PFA). We use
to this aim the scattering formalism which is nowadays the best tool available
for accurate and reliable theory-experiment comparisons. We first recall the
main lines of this formalism when the mirrors can be considered to obey
specular reflection. We then discuss the more general case where non planar
mirrors give rise to non-specular reflection with wavevectors and field
polarisations mixed. The general formalism has already been fruitfully used for
evaluating the effect of roughness on the Casimir force as well as the lateral
Casimir force or Casimir torque appearing between corrugated surfaces. In this
short review, we focus our attention on the case of the lateral force which
should make possible in the future an experimental demonstration of the
nontrivial (i.e. beyond PFA) interplay of geometry and Casimir effect.Comment: corrected typos, added references, QFEXT'07 special issue in J. Phys.
Ferromagnetic redshift of the optical gap in GdN
We report measurements of the optical gap in a GdN film at temperatures from
300 to 6K, covering both the paramagnetic and ferromagnetic phases. The gap is
1.31eV in the paramagnetic phase and red-shifts to 0.9eV in the spin-split
bands below the Curie temperature. The paramagnetic gap is larger than was
suggested by very early experiments, and has permitted us to refine a
(LSDA+U)-computed band structure. The band structure was computed in the full
translation symmetry of the ferromagnetic ground state, assigning the
paramagnetic-state gap as the average of the majority- and minority-spin gaps
in the ferromagnetic state. That procedure has been further tested by a band
structure in a 32-atom supercell with randomly-oriented spins. After fitting
only the paramagnetic gap the refined band structure then reproduces our
measured gaps in both phases by direct transitions at the X point.Comment: 5 pages, 4 figure
Second harmonic generation in SiC polytypes
LMTO calculations are presented for the frequency dependent second harmonic
generation (SHG) in the polytypes 2H, 4H, 6H, 15R and 3C of SiC. All
independent tensor components are calculated. The spectral features and the
ratios of the 333 to 311 tensorial components are studied as a function of the
degree of hexagonality. The relationship to the linear optical response and the
underlying band structure are investigated. SHG is suggested to be a sensitive
tool for investigating the near band edge interband excitations.Comment: 12 pages, 10 figure
Size quantization effects in thin film Casimir interaction
We investigate the role of size quantization in the vacuum force between
metallic films of nanometric thickness. The force is calculated by the Lifshitz
formula with the film dielectric tensor derived from the one-electron energies
and wavefunctions under the assumption of a constant potential inside the film
and a uniform distribution of the positive ion charge. The results show that
quantization effects tend to reduce the force with respect to the continuum
plasma model. The reduction is more significant at low electron densities and
for film size of the order of few nanometers and persists for separation
distances up to 10 nm. Comparison with previous work indicates that the
softening of the boundary potential is important in determining the amount of
the reduction. The calculations are extended to treat Drude intraband
absorption. It is shown that the inclusion of relaxation time enhances the size
quantization effects in the force calculations
Energy focusing inside a dynamical cavity
We study the exact classical solutions for a real scalar field inside a
cavity with a wall whose motion is self-consistently determined by the pressure
of the field itself. We find that, regardless of the system parameters, the
long-time solution always becomes nonadiabatic and the field's energy
concentrates into narrow peaks, which we explain by means of a simple
mechanical system. We point out implications for the quantized theory.Comment: 5 pages, 6 figures, double column, submitted to P.R.
Spin-dependent resonant tunneling through semimetallic ErAs quantum wells
Resonant tunneling through semimetallic ErAs quantum wells embedded in GaAs
structures with AlAs barriers was recently found to exhibit an intriguing
behavior in magnetic fields which is explained in terms of tunneling selection
rules and the spin-polarized band structure including spin-orbit coupling.Comment: 4 pages, figures supplied as self-unpacking figures.uu, uses
epsfig.sty to incorporate figures in preprin
Casimir interaction: pistons and cavity
The energy of a perfectly conducting rectangular cavity is studied by making
use of pistons' interactions. The exact solution for a 3D perfectly conducting
piston with an arbitrary cross section is being discussed.Comment: 10 pages, 2 figures, latex2
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