arXiv subjects

J. J. Saenz

Publications and source records attributed to J. J. Saenz.

At least 19 recordsLinked to original sources

arXiv2015

Localized magnetic plasmons in all-dielectric mu<0 metastructures

Metamaterials are known to exhibit a variety of electromagnetic properties non-existing in nature. We show that an all-dielectric (non-magnetic) system consisting of deep subwavelength, high permittivity resonant spheres possess effective negative magnetic permeability (dielectric permittivity being positive and small). Due to the symmetry of the electromagnetic wave equations in classical electrodynamics, localized "magnetic" plasmon resonances can be excited in a metasphere made of such metamaterial. This is theoretically demonstrated by the coupled-dipole approximation and numerically for real spheres, in full agreement with the exact analytical solution for the scattering process by the same metasphere with effective material properties predicted by effective medium theory. The emergence of this phenomenon as a function of structural order within the metastructures is also studied. Universal conditions enabling effective negative magnetic permeability relate subwavelength sphere permittivity and size with critical filling fraction. Our proposal paves the way towards (all-dielectric) magnetic plasmonics, with a wealth of fascinating applications.

physics.optics↗

arXiv2014

Statistical scattering of waves in disordered waveguides: The limiting macroscopic statistics in the ballistic regime

In this work, we present a theoretical study of the statistical properties of wave scattering in a disordered ballistic waveguide of length L; we have called this system the "building block". The building block is interesting as a physical system because its statistical properties could be studied experimentally in the laboratory. In order to study the building block, as a physical system in itself, we have developed a perturbative method based on Born series. This method is valid only in the ballistic regime, when the length of the system L is smaller than the mean free path l, and in the short-wave-length approximation, when the the wave number k and the mean free path l satisfy kl >> 1. This method has allowed to find, analytically, the behavior of quantities of interest that we have not been able to find from the diffusion equation. In contrast with the diffusion equation method, which takes into account approximately the contribution of closed channels, this method takes them explicitly. In earlier works numerical evidence was found that the expectation values of some interesting quantities are insensitive to the number of closed channels that were used on the calculations; with this method, we could show that closed channels are relevant for the expectation values of amplitudes but irrelevant for the intensities and conductance expectation values. The results of this method show a good agreement with numerical simulations.

cond-mat.mes-hall↗

arXiv2012

Negative scattering asymmetry parameter for dipolar particles: Unusual reduction of the transport mean free path and radiation pressure

We establish a relationship between the electric magnetic dipole interaction force from a plane wave on a small magnetodielectric particle, the transport cross-section and the scattering asymmetry parameter, g. In this way, we predict negative g that minimize the transport mean free-path below values of the scattering mean free path of a dilute suspension of both perfectly reflecting spheres as well as of those that satisfy the so-called Kerker conditions, like high permittivity dielectric ones.

cond-mat.mtrl-sci↗

arXiv2012

Angle-Suppressed Scattering and Optical Forces on Submicron Dielectric Particles

We show that submicron Silicon spheres, whose polarizabilities are completely given by their two first Mie coefficients, are an excellent laboratory to test effects of both angle-suppressed and resonant differential scattering cross sections. Specifically, outstanding scattering angular distributions, with zero forward or backward scattered intensity, (i.e., the so-called Kerker's conditions), previously discussed for hypothetical magnetodielectric particles, are now observed for those Si objects in the near infrared. Interesting new consequences for the corresponding optical forces are derived from the interplay, both in and out resonance, between the electric and magnetic induced dipoles.

physics.optics↗

arXiv2012

Optical forces from an evanescent wave on a magnetodielectric small particle

We report the first study on the optical force exerted by an evanescent wave on a small sphere with both electric and magnetic response to the incident field, immersed in an arbitrary nondissipative medium. New expressions and effects from their gradient, radiation pressure, and curl components are obtained due to the particle induced electric and magnetic dipoles, as well as to their mutual interaction. We predict possible dramatic changes in the force depending on either the host medium, the polarization and the nature of the surface wave.

physics.optics↗

arXiv2010

Strong magnetic response of submicron Silicon particles in the infrared

High-permittivity dielectric particles with resonant magnetic properties are being explored as constitutive elements of new metamaterials and devices in the microwave regime. Magnetic properties of low-loss dielectric nanoparticles in the visible or infrared are not expected due to intrinsic low refractive index of optical materials in these regimes. Here we analyze the dipolar electric and magnetic response of loss-less dielectric spheres made of moderate permittivity materials. For low material refractive index there are no sharp resonances due to strong overlapping between different multipole contributions. However, we find that Silicon particles with refractive index 3.5 and radius approx. 200nm present a dipolar and strong magnetic resonant response in telecom and near-infrared frequencies, (i.e. at wavelengths approx. 1.2-2 micrometer). Moreover, the light scattered by these Si particles can be perfectly described by dipolar electric and magnetic fields, quadrupolar and higher order contributions being negligible.

physics.optics↗

arXiv2008

On the density of states and extinction mean free path of waves in random media: Dispersion relations and sum rules

We establish a fundamental relationship between the averaged density of states and the extinction mean free path of wave propagating in random media. From the principle of causality and the Kramers-Kronig relations, we show that both quantities are connected by dispersion relations and are constrained by a frequency sum rule. The results are valid under very general conditions and should be helpful in the analysis of measurements of wave transport through complex systems and in the design of randomly or periodically structured materials with specific transport properties.

cond-mat.dis-nn↗

arXiv2007

Full transmission through perfect-conductor subwavelength hole arrays

Light transmission through 2D subwavelength hole arrays in perfect-conductor films is shown to be complete (100%) at some resonant wavelengths even for arbitrarily narrow holes. Conversely, the reflection on a 2D planar array of non-absorbing scatterers is shown to be complete at some wavelengths regardless how weak the scatterers are. These results are proven analytically and corroborated by rigorous numerical solution of Maxwell's equations. This work supports the central role played by dynamical diffraction during light transmission through subwavelength hole arrays and it provides a systematics to analyze more complex geometries and many of the features observed in connection with transmission through hole arrays.

cond-mat.other↗

arXiv2006

Statistical Scattering of Waves in Disordered Waveguides: from Microscopic Potentials to Limiting Macroscopic Statistics

We study the statistical properties of wave scattering in a disordered waveguide. The statistical properties of a "building block" of length (delta)L are derived from a potential model and used to find the evolution with length of the expectation value of physical quantities. In the potential model the scattering units consist of thin potential slices, idealized as delta slices, perpendicular to the longitudinal direction of the waveguide; the variation of the potential in the transverse direction may be arbitrary. The sets of parameters defining a given slice are taken to be statistically independent from those of any other slice and identically distributed. In the dense-weak-scattering limit, in which the potential slices are very weak and their linear density is very large, so that the resulting mean free paths are fixed, the corresponding statistical properties of the full waveguide depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. Our final result is a diffusion equation in the space of transfer matrices of our system, which describes the evolution with the length L of the disordered waveguide of the transport properties of interest. In contrast to earlier publications, in the present analysis the energy of the incident particle is fully taken into account.

cond-mat.mtrl-sci↗

arXiv2005

Site and lattice resonances in metallic hole arrays

A powerful analytical approach is followed to study light transmission through subwavelength holes drilled in thick perfect-conductor films, showing that full transmission (100%) is attainable in arrays of arbitrarily narrow holes as compared to the film thickness. The interplay between resonances localized in individual holes and lattice resonances originating in the array periodicity reveals new mechanisms of transmission enhancement and suppression. In particular, localized resonances obtained by filling the holes with high-index-of-refraction material are examined and experimentally observed through large enhancement in the transmission of individual holes.

cond-mat.mtrl-sci↗

arXiv2005

Electromagnetic surface states in structured perfect-conductor surfaces

Surface-bound modes in metamaterials forged by drilling periodic hole arrays in perfect-conductor surfaces are investigated by means of both analytical techniques and rigorous numerical solution of Maxwell's equations. It is shown that these metamaterials cannot be described in general by local, frequency-dependent permittivities and permeabilities for small periods compared to the wavelength, except in certain limiting cases that are discussed in detail. New related metamaterials are shown to exhibit exciting optical properties that are elucidated in the light of our simple analytical approach.

cond-mat.mtrl-sci↗

arXiv2002

Quantum Conductance in Semimetallic Bismuth Nanocontacts

Electronic transport properties of bismuth nanocontacts are analyzed by means of a low temperature scanning tunneling microscope. The subquantum steps observed in the conductance versus elongation curves give evidence of atomic rearrangements in the contact. The underlying quantum nature of the conductance reveals itself through peaks in the conductance histograms. The shape of the conductance curves at 77 K is well described by a simple gliding mechanism for the contact evolution during elongation. The strikingly different behaviour at 4 K suggests a charge carrier transition from light to heavy ones as the contact cross section becomes sufficiently small.

cond-mat.mes-hall↗

arXiv2001

Universal Conductance Distributions in the Crossover between Diffusive and Localization Regimes

The full distribution of the conductance $P(G)$ in quasi-one-dimensional wires with rough surfaces is analyzed from the diffusive to the localization regime. In the crossover region, where the statistics is dominated by only one or two eigenchannels, the numerically obtained P(G) is found to be independent of the details of the system with the average conductance as the only scaling parameter. For < e^2/h, P(G) is given by an essentially ``one-sided'' log-normal distribution. In contrast, for e^2/h < <= 2e^2/h, the shape of P(G) remarkable agrees with those predicted by random matrix theory for two fluctuating transmission eigenchannels.

cond-mat.dis-nn↗

arXiv2001

Resonant radiation pressure on neutral particles in a waveguide

A theoretical analysis of electromagnetic forces on neutral particles in an hollow waveguide is presented. We show that the effective scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induce a resonant enhanced backscattering state of the scatterer-guide system close to the onset of new modes. The particle effective cross section can then be as large as the wavelength even far from any transition resonance. As we will show, a small particle can be strongly accelerated along the guide axis while being highly confined in a narrow zone of the cross section of the guide.

physics.optics↗

arXiv2000

Electronic Transmission Through Metallic Nanowires: Generalized Scattering Matrix Approach

An easy to implement and powerful method for the solution of 3D scattering problems that can be well described by Helmholtz equation is presented. The matrix algebra used provides excellent stability versus the number of junctions as well as great computational speed. The matrix truncation method yields an easy single-parameter convergence procedure. Subsequently, some aspects of the electronic transport through metal nanowires are studied by the use of Landauer's scattering approach to the conductance. We predict the existence of current vortex-rings patterns due to sharp enough narrow-wide connections in atomic size point contacts. Longitudinal resonances between scattering centers provide a simple physical picture for the understanding of negative differential resistance in ideal monoatomic contacts. Relatively long nanowires with high geometrical perfection -like those recently observed by Transmission Electron Microscopy- are modelled exhibiting resonant tunnelling and total reflection at given incident energy intervals.

cond-mat.mes-hall↗

arXiv1998

Statistical Distribution of Intensities Reflected from Disordered Media

A theoretical analysis of the statistical distributions of the reflected intensities from random media is presented. We use random matrix theory to analytically deduce the probability densities in the localization regime. Numerical calculations of the coupling to backward modes in surface corrugated waveguides are also put forward for comparison. Interestingly, the speckle distributions are found to be independent of the transport regime. Despite the scattering being highly non-isotropic, the predicted probability densities reproduce accurately the numerical results.

cond-mat.dis-nn↗

arXiv1998

Intensity Distribution of Modes in Surface Corrugated Waveguides

Exact calculations of transmission and reflection coefficients in surface randomly corrugated optical waveguides are presented. As the length of the corrugated part of the waveguide increases, there is a strong preference to forward coupling through the lowest mode. An oscillating behavior of the enhanced backscattering as a function of the wavelength is predicted. Although the transport is strongly non isotropic, the analysis of the probability distributions of the transmitted waves confirms in this configuration distributions predicted by Random Matrix Theory for volume disorder.

cond-mat.dis-nn↗

arXiv1998

Transition from Diffusive to Localized Regimes in Surface Corrugated Optical Waveguides

Exact calculations of the transmittance of surface corrugated optical waveguides are presented. The elastic scattering of diffuse light or other electromagnetic waves from a rough surface induces a diffusive transport along the waveguide axis. As the length of the corrugated part of the waveguide increases, a transition from the diffusive to the localized regime is observed. This involves an analogy with electron conduction in nanowires, and hence, a concept analogous to that of ``resistance'' can be introduced. We show an oscillatory behavior of both the elastic mean free path and the localization length versus the wavelength.

cond-mat.mes-hall↗