R. Moussa

Numerical study of the one-dimensional Hubbard model in determination of trans-polyacetylene properties

Abstract Quantum Monte Carlo simulation on one-dimensional Hubbard model is developed to study the effect of electron–electron interaction on trans-polyacetylene (t-PA) properties. The numerical calculation is based on the evaluation of the trace of the partition function using a special version of the so-called determinantal method. We use the Blakenbecler, Scalapino, Sugar and Hirsch (BSSH) algorithm based on the Hubbard–Stratonovich transformation to overcome the original problem involving anticommuting fermion operators. This numerical study allowed us to calculate mean values of different observables of physical interest such as the energies and their fluctuations. The behavior of quantum fluctuations is confirmed and interpreted by determining the specific heat. The system exhibits different ordering depending on different ranges of repulsion energy of Coulomb (U) and the on-site energy (E).

Numerical study on localized defect modes in two-dimensional lattices: a high Q-resonant cavity

Abstract The spectral widths and the quality factors of defect modes localized for different defects structures formed in a 2D photonic crystal composed of a square lattice of circular rods of indium antimonide (InSb) are theoretically investigated. It is first shown that some factors such as the lattice nature, the line defect orientation, the nature and the defect width have a significant influence on the optical properties of the studied structures and can improve the Q factor and defect peak transmission intensity. Particularly, the transmission spectra of the defects calculated by means the transfer-matrix-method for a particular structure of eight line defects introduced in its center showed a high-quality factor which exceeded 4×10 5 . This is an important issue for the fabrication of photonic crystals with such desired properties.

Photonic band gaps in highly ionic medium: Cucl, CuBr, CuI

Abstract Using the transfer-matrix-method, we have studied the propagation of electromagnetic waves through two-dimensional (2D) and three-dimensional (3D) dispersive photonic band gap (PBG) structures constructed from copper halides materials, especially from CuCl compounds. A special attention has been paid to the effect of the polariton gap on the PBG properties. This study reveals that “Twin gaps” and “Twin brothers” concepts and the flattened bands phenomena in both polarizations and for both structures (i.e. 2D and 3D) are all consequences of the strong photon–phonon coupling, particularly near the long wave length transverse optical phonon frequency. Furthermore, results for comparison of CuCl PBG materials with whose of the other copper halides (i.e. CuBr and CuI) are reported.

Nitride compounds as photonic crystals in the optical region

Usin the transfer matrix method we have studied the optical properties related to the photonic band gap (PBG) concept of the III-nitride family particularly InN and AlN. We have shown that these materials present, for a particular lattice constant and for the same structure, PBGs in all near infrared, optical and ultaviolet regions. In order to give optimal conditions for experiments, the number and the width of these PBGs are studied in more detail. The case of the absorption which occurs for the higher lattice parameter is discussed. This novel class of material opens up many potential applications. For example, PBG crystals can be used to inhibit spontaneous emission in photonic devices, leading to more efficient light emitters such as single-mode-light emitting diodes.

Large photonic band gap's in one-dimensional multilayer structures

A one-dimensional photonic lattice constructed from a material possessing a higher value of dielectric constant has been studied under the consideration of photonic band gap, filling fraction, and the competition of different transmission mechanism of the incoming electromagnetic waves. A special attention has been paid to the localized state introduced by the introduction of defect in our multilayer structure.

Studying structural, electronic and optical properties of zinc-blende Ga1−x Al x P at normal and under pressure by means of first principle

Structural, electronic and optical properties of the zinc-blende Ga1−x Al x P ternary alloys with their ordered AlP and GaP binary compounds have been investigated, using the full potential linearized augmented plane wave method in conjunction with the density functional theory. The total energies are carried out to calculate the lattice constant, bulk modulus and its pressure derivative of the zinc-blende AlP, GaP binary compounds and their corresponding ternary Ga1−x Al x P solid solutions for the compositions (x = 0.25, 0.50 and 0.75). The band gap energies and the optical properties of these materials are investigated at normal pressure condition as well as under high pressure levels. The estimated results obtained from this work are justified, discussed and compared with the experimental data and other available theoretical works.

Photonic Band Structures of Two‐ and Three‐Dimensional Periodic Dielectric Materials

By the use of the Transfer-Matrix-Method (TMM) we have calculated both photonic band structure and transmission coefficient for electromagnetic waves of S and P polarization propagating in two-dimensional 2D structures consisting of identical parallel alumina dielectric cylinders in a square lattice. We have also studied the existence of photonic band gaps of air cylinders formed in a slab of methylpentene polymer in the far-infrared region. Furthermore, the case of dielectric spheres in a three-dimensional 3D cubic lattice and the effect of the discretization mesh in the TMM was discussed.

First-Principle Study of the Structural, Electronic, and Optical Properties of Cubic InNxP1–x Ternary Alloys under Hydrostatic Pressure

Abstract In this article, we present results of the first-principle study of the structural, electronic, and optical properties of the InN, InP binary compounds and their related ternary alloy InNxP1–x in the zinc-blend (ZB) phase within a nonrelativistic full potential linearised augmented plan wave (FP-LAPW) method using Wien2k code based on the density functional theory (DFT). Different approximations of exchange–correlation energy were used for the calculation of the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. Whereas the lattice constant decreases with increasing nitride composition x. Our results present a good agreement with theoretical and experimental data. The electronic band structures calculated using Tran-Blaha-modified Becke–Johnson (TB-mBJ) approach present a direct band gap semiconductor character for InNxP1–x compounds at different x values. The electronic properties were also calculated under hydrostatic pressure for (P=0.00, 5.00, 10.0, 15.0, 20.0, 25.0 GPa) where it is found that the InP compound change from direct to indirect band gap at the pressure P≥7.80 GPa. Furthermore, the pressure effect on the dielectric function and the refractive index was carried out. Results obtained in our calculations present a good agreement with available theoretical reports and experimental data.