Anomalous Stark effect on excitonic states in a preionization electric field

The low-temperature (T=80 K) excitonic light reflection spectra of CdS crystals in the electric field of a Schottky barrier are investigated. An anomalous Stark shift of the hydrogen-like excitonic state in the preionization limit is recorded for the first time. The distribution of the subbarrier electric field is determined from an analysis of the spectra performed on the basis of the theory of nonlocal dielectric response in a spatially inhomogeneous medium. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 38–42 (10 July 1996)     

On Solvable Normal Subgroups of Finite Groups

We consider solvable invariant subgroups of a finite group with bounded primary indices of maximal subgroups. We establish that an invariant subgroup of this type belongs to the product of classical formations and investigate its dispersibility.     

Photoluminescence of thin amorphous-nanocrystalline silicon films

Photoluminescence spectra of thin hydrogenated-silicon films having mixed amorphous-nanocrystalline phase composition have been studied. Fabry-Perot interference was found to affect strongly the shape of the spectra. An analysis of the spectra made with inclusion of interference corrections shows that only one emission band forms in the 0.6–1.0 μm region due to carrier recombination at centers of the same type. Fiz. Tverd. Tela (St. Petersburg) 41, 153–158 (January 1999)     

Minimal Hereditary ω-Local Non-ℌ-Formations

We describe minimal hereditary -local non--formations, where is a formation of the classical type.     

Ultrafast optical switching in three-dimensional photonic crystals

We present the first experimental investigation of ultrafast optical switching in a three-dimensional photonic crystal made of a Si-opal composite. Ultrafast (30 fs) changes in reflectivity around the photonic stop band up to 1% were measured for moderate pump power (70 microJ/cm(2)). Short-lived photoexcited carriers in silicon induce changes in the dielectric constant of Si and diminish the constructive interference inside the photonic crystal. The results are analyzed within a model based on a two-band mixing formalism.     

Resonant behavior and selective switching of stop bands in three-dimensional photonic crystals with inhomogeneous components

We demonstrate that, in contrast with the well-studied photonic crystals consisting of two homogeneous components, photonic crystals comprised of inhomogeneous or multiple (three or more) components may bring new opportunities to photonics due to the discovered quasiperiodic resonant behavior of their (hkl) stop bands as a function of the reciprocal lattice vector. A resonant stop band cannot be switched off for any permittivity of structural components. Tuning the permittivity or structural parameters allows the selective on-off switching of nonresonant (hkl) stop bands. This independent manipulation of light at different Bragg wavelengths provides a new degree of freedom to design selective optical switches and waveguides. Transmission experiments performed on synthetic opals confirmed the theoretical predictions.     

Resonant elastic scattering of light from single quantum wells in semiconductor multilayers

A theory is developed for steady-state elastic scattering of light via quasi-2D excitons from a quantum well (QW) whose interfaces are randomly rough. The study is mainly focused on the angle dependences of radiation giving direct information about static disorder responsible for the elastic scattering. A nonlocal excitonic susceptibility is expressed in terms of random profile functions of QW interfaces. Treated is elastic scattering of light from a disordered QW in the following actual dielectric environments: (i) a uniform background, (ii) a Fabry–Perot film with rough boundaries, and (iii) a semiconductor microcavity. The cross-sections are derived analytically for scattering of linearly polarized light to the lowest (Born's) approximation with arbitrary roughness statistics. The spectral and angle dependencies of scattering intensity are analyzed numerically in the absolute-value scale with Gaussian correlation of interface roughness. The probability 10⁻² was found for the exciton-mediated scattering of a photon from a QW interface roughness whose root-mean-square height is on the level of 2×10⁻¹ nm. This probability is shown to exceed by two orders of magnitude that is typical of resonant scattering from either a single semiconductor surface or rough boundaries of a semiconductor Fabry–Perot film containing the QW. The scattering spectrum of a QW placed in a microcavity is predicted to have a doublet structure whose components are associated with the cavity exciton–polaritons.