arXiv subjects

E. N. Economou

Publications and source records attributed to E. N. Economou.

29 records · Page 2Linked to original sources

arXiv2004

Effective medium theory of left-handed materials

We analyze the transmission and reflection data obtained through transfer matrix calculations on metamaterials of finite lengths, to determine their effective permittivity and permeability. Our study concerns metamaterial structures composed of periodic arrangements of wires, cut-wires, split ring resonators (SRRs), closed-SRRs, and both wires and SRRs. We find that the SRRs have a strong electric response, equivalent to that of cut-wires, which dominates the behavior of left-handed materials (LHM). Analytical expressions for the effective parameters of the different structures are given, which can be used to explain the transmission characteristics of LHMs. Of particular relevance is the criterion introduced by our studies to identify if an experimental transmission peak is left- or right-handed.

cond-mat.mtrl-sci↗

arXiv2002

Refraction at Media with Negative Refractive Index

We show that an electromagnetic (EM) wave undergoes negative refraction at the interface between a positive and negative refractive index material. Finite difference time domain (FDTD) simulations are used to study the time evolution of an EM wave as it hits the interface. The wave is trapped temporarily at the interface and after a long time, the wave front moves eventually in the negative direction. This explains why causality and speed of light are not violated in spite of the negative refraction always present in a negative index material.

cond-mat↗

arXiv2000

Gap deformation and classical wave localization in disordered two-dimensional photonic band gap materials

By using two ab initio numerical methods we study the effects that disorder has on the spectral gaps and on wave localization in two-dimensional photonic band gap materials. We find that there are basically two different responses depending on the lattice realization (solid dielectric cylinders in air or vise versa), the wave polarization, and the particular form under which disorder is introduced. Two different pictures for the photonic states are employed, the ``nearly free'' photon and the ``strongly localized'' photon. These originate from the two different mechanisms responsible for the formation of the spectral gaps, ie. multiple scattering and single scatterer resonances, and they qualitatively explain our results.

cond-mat.dis-nn↗

arXiv1999

Kinetic and Transport Equations for Localized Excitations in Sine-Gordon Model

We analyze the kinetic behavior of localized excitations - solitons, breathers and phonons - in Sine-Gordon model. Collision integrals for all type of localized excitation collision processes are constructed, and the kinetic equations are derived. We analyze the kinetic behavior of localized excitations - solitons, breathers and phonons - in Sine-Gordon model. Collision integrals for all type of localized excitation collision processes are constructed, and the kinetic equations are derived. We prove that the entropy production in the system of localized excitations takes place only in the case of inhomogeneous distribution of these excitations in real and phase spaces. We derive transport equations for soliton and breather densities, temperatures and mean velocities i.e. show that collisions of localized excitations lead to creation of diffusion, thermoconductivity and intrinsic friction processes. The diffusion coefficients for solitons and breathers, describing the diffusion processes in real and phase spaces, are calculated. It is shown that diffusion processes in real space are much faster than the diffusion processes in phase space.

solv-int↗

arXiv1998

One-Dimensional Extended States in Partially Disordered Planar Systems

We obtain analytically a continuum of one-dimensional ballistic extended states in a two-dimensional disordered system, which consists of compactly coupled random and pure square lattices. The extended states give a marginal metallic phase with finite conductivity $σ_{0}=2e^2/h$ in a wide energy range, whose boundaries define the mobility edges of a first-order metal-insulator transition. We show current-voltage duality, $H_{\parallel}/T$ scaling of the conductivity in parallel magnetic field $H_{\parallel}$ and non-Fermi liquid properties when long-range electron-electron interactions are included.

cond-mat.dis-nn↗

arXiv1998

Comment on "Energy Velocity of Diffusion Waves in Strongly Scattering Media"

A comment on the recently published article (PRL 79, 3166 (1997)) is given. The issue is if there is a unique self-consistent way in determining the effective medium in a random medium. The recently introduced effective medium theory (PRL 75, 3442 (1995)) based on the principle of energy density homogenization is also discussed.

cond-mat.dis-nn↗

arXiv1998

Tight-binding parameterization for photonic band gap materials

The ideas of the linear combination of atomic orbitals (LCAO) method, well known from the study of electrons, is extended to the classical wave case. The Mie resonances of the isolated scatterer in the classical wave case, are analogous to the localized eigenstates in the electronic case. The matrix elements of the two-dimensional tight-binding (TB) Hamiltonian are obtained by fitting to ab initio results. The transferability of the TB model is tested by reproducing accurately the band structure of different 2D lattices, with and without defects, thus proving that the obtained TB parameters can be used to study other properties of the photonic band gap materials.

cond-mat.dis-nn↗

arXiv1997

Anisotropic Quantum Transport in Layered High--$T_c$ Cuprates

A random lattice model with dilute interlayer bonds of density $p$ is proposed to describe the underdoped high--$T_c$ cuprates. We show analytically via an appropriate perturbation expansion and verify independently by numerical scaling of the conductance that for any finite $p$ the states remain extended in all directions, despite the presence of interlayer disorder. However, the obtained electronic transport is highly anisotropic with violent conductance fluctuations occuring in the layering direction, which can be responsible for the experimentally observed metallic "in-plane" and semiconducting "out-of-plane" resistivity of the cuprates.

cond-mat.dis-nn↗

arXiv1997

Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides

We examine the effect on the DC resistivity of small-q electron-phonon scattering, in a system with the electronic topology of the high-T_c oxides. Despite the fact that the scattering is dominantly forward, its contribution to the transport can be significant due to ``ondulations'' of the bands in the flat region and to the umpklapp process. When the extended van-Hove singularities are sufficiently close to $E_F$ the acoustic branch of the phonons contribute significantly to the transport. In that case one can obtain linear $T$ dependent resistivity down to temperatures as low as 10 K, even if electrons are scattered also by optical phonons of about 500 K as reported by Raman measurements.

cond-mat.supr-con↗

arXiv1997

Localization in Highly Anisotropic Systems

The localization behavior of the Anderson model with anisotropic hopping integral t for weakly coupled planes and weakly coupled chains is investigated both numerically with the transfer matrix method and analytically within the self-consistent theory of localization. It is found that the mobility edge is independent of the propagating direction. However, the correlation (localization) length in the extended (localized) side of the transition can be very different for the two directions. The critical disorder W$_c$ is found to vary from t$^{1 \over 4}$ for weakly coupled planes to t$^{1 \over 2}$ for weakly coupled chains.

cond-mat↗

arXiv1997

Scaling Properties in Highly Anisotropic Systems

Scaling of the conductances and the finite-size localization lengths is generalized to anisotropic systems and tested in two dimensional systems. Scaling functions of isotropic systems are recovered once the dimension of the system in each direction is chosen to be proportional to the localization length. It is also shown that the geometric mean of the localization lengths is a function of the geometric mean of the conductivities. The ratio of the localization lengths is proportional to the square root of the ratio of the conductivities, which in turn is proportional to the anisotropy strength t, in the weak scattering limit.

cond-mat↗