W. Luis Mochan

Exact surface impedance formulation of the Casimir force: application to spatially dispersive metals

We show that exact results are obtained for the calculation of Casimir forces between arbitrary materials using the concept of surface impedances, obtaining in a trivial way the force in the limit of perfect conductors and also Lifshitz formula in the limit of semi-infinite media. As an example we present a full and rigorous calculation of the Casimir force between two metallic half-spaces described by a hydrodynamic nonlocal dielectric response.

Optical properties of bimetallic superlattices

Abstract We apply the transfer matrix formalism to study the local optical properties of bimetallic superlattices. We also study the surface modes coupling of the sandwich geometry (three layer system). We calculate the dispersion relation of the collective normal modes of an infinite superlattice and the reflectance of a semi-infinite superlattice for p-polarized light. The results of the dispersion relation show two branches of the surface plasmon-polaritons and the reflectance presents two well defined minima due to the surface modes coupling of the succesive metallic layers. The coupling is strong for thin layers, but becomes weak as the layer thickness becomes large. The reflectance of the sandwich geometry presents two minima which are due to the excitation of the symmetric and antisymm e tric surface plasmon-polaritons. The parameters used here correspond to Al and Mg.

Bound state spectroscopy of He adsorbed on NaCl(001): band structure effects

Abstract The interaction between atoms and surfaces may be probed by bound state resonance spectroscopy. The experiments are usually interpreted within the free particle picture which assumes that the energy-momentum relation of atoms adsorbed onto a surface is described by 2D parabolic bands. We calculate and analyze the band structure of an atom adsorbed on a model corrugated surface and follow its behavior as the interaction potential evolves from weakly to strongly corrugated. Besides the expected reduction of degeneracy and development of gaps, we obtained a sizable correction to the bound state energies. We employ our results to reanalyze the available experiments on the system HeNaCl(001).

Effective optical response of metamaterials

We use a homogenization procedure for Maxwell’s equations in order to obtain in the local limit the frequency-dependent macroscopic dielectric-response tensor ij of metamaterials made of a matrix with inclusions of any geometrical shape repeated periodically with any lattice structure. We illustrate the formalism calculating ij for several structures. For dielectric rectangular inclusions within a conducting material we obtain an anisotropic response that may change from conductorlike at low to dielectriclike with resonances at large , attaining a very small reflectance at intermediate frequencies which can be tuned through geometrical tailoring. A simple explanation allowed us to predict and confirm similar behavior for other shapes, even isotropic, close to the percolation threshold.

Surface screening in the Casimir force

We calculate the corrections to the Casimir force between two metals due to the spatial dispersion of their response functions. We employ model-independent expressions for the force in terms of the optical coefficients. We express the nonlocal corrections to the Fresnel coefficients employing the surface d{sub perpendicular} parameter, which accounts for the distribution of the surface screening charge. Within a self-consistent jellium calculation, spatial dispersion increases the Casimir force significatively for small separations. The nonlocal correction has the opposite sign than previously predicted employing hydrodynamic models and assuming abruptly terminated surfaces.

Macroscopic optical response and photonic bands

We develop a formalism for the calculation of the macroscopic dielectric response of composite systems made of particles of one material embedded periodically within a matrix of another material, each of which is characterized by a well-defined dielectric function. The nature of these dielectric functions is arbitrary, and could correspond to dielectric or conducting, transparent or opaque, absorptive and dispersive materials. The geometry of the particles and the Bravais lattice of the composite are also arbitrary. Our formalism goes beyond the long-wavelength approximation as it fully incorporates retardation effects. We test our formalism through the study of the propagation of electromagnetic waves in two-dimensional photonic crystals made of periodic arrays of cylindrical holes in a dispersionless dielectric host. Our macroscopic theory yields a spatially dispersive macroscopic response which allows the calculation of the full photonic band structure of the system, as well as the characterization of its normal modes, upon substitution into the macroscopic field equations. We can also account approximately for the spatial dispersion through a local magnetic permeability and analyze the resulting dispersion relation, obtaining a region of left handedness.

Atom-surface band structure and bound-state resonances A theoretical study

The energy bands of an atom adsorbed on a crystalline surface have been calculated for representative hypothetical systems. The corrugation corresponding to the atom-surface interaction potential of several of the studied systems is similar to the corrugation reported for systems in which the surface holds a layer of adsorbed particles. Characteristic features of the band structure, that depend on the corrugation of the atom-surface interaction potential and on the depth of the associated bound-state, have been found. The bands of all the systems evolve to parabolic shaped bands displaced downwards with respect to the corresponding freeatom parabolic bands. Theoretical studies of atom-surface elastic scattering revealed that bound-state resonances do not appear if the energy of the incident atoms is not high enough to reach the region where the band is parabolic. O 1998 Elsevier Science B.V. All rights reserved.

UNCERTAINTY RELATIONS FOR A DEFORMED OSCILLATOR

We construct a deformed oscillator whose energy spectra is similar to that of a Morse potential. We obtain a convenient algebraic representation of the displacement and the momentum of a Morse oscillator by expanding them in terms of deformed creation and annihilation operators and we compute their average values between approximate coherent states of the deformed oscillator, and we compare them to the results obtained using the exact Morse coordinate and momenta. Finally we evaluate the temporal evolution of the dispersion (Δx)(Δp) and show that these states are not minimum uncertainty states.

On the apparent superluminality of evanescent waves

There have been many recent theoretical and experimental reports on the propagation of light pulses at speeds exceeding the speed of light in vacuum

Nonadditivity of poynting vector within opaque media.

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