Modern Physics Letters B

A new, wide class of relativistic stochastic processes is introduced. All relativistic processes considered so far in the literature (the Relativistic Ornstein–Uhlenbeck Process as well as the Franchi–Le Jan and the Dunkel–Hänggi processes) are members of this class. The stochastic equations of motion and the associated forward Kolmogorov equations are obtained for each process in the class. The corresponding manifestly covariant transport equation is also obtained. In particular, the manifestly covariant equations for the Franchi–Le Jan and the Dunkel–Hänggi processes are derived here for the first time. Finally, the manifestly covariant approach is used to prove a new H-theorem for all processes in the class.

We investigate optical bistability in intersubband transitions of an asymmetric semiconductor quantum well structure that has equidistant transitions between three subbands of the system and is placed in a unidirectional cavity. The system is simultaneously coupled by a fundamental field and its second harmonic. The second harmonic field acts as a control field and significantly influences the optical bistability. In addition, the two-color coherent control of optical bistability by the relative phase of the fundamental and the second harmonic fields is shown. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the SQW solid-state system, which is much more practical than that in the atomic system because of its flexible design and the controllable interference strength.

The authors investigate the geometric phase of a spin-J system interacting with a classical magnetic field which contains a fluctuating component. Assuming an Ornstein–Uhlenbeck process for the fluctuations, we find that the distribution due to the fluctuating component for the geometric phase is a Gaussian. We calculate in detail the variance of geometric and dynamic phases. The results clearly show that the geometric phase can reduce the fluctuations, but the dynamic phase can not.

P-type porous SiC layers were fabricated by anodization of a hot-pressed p-type 6H-SiC (30 kΩcm) and a 1.6 μm SiC film was deposited onto p-type Si(100) substrate by Pulsed Laser Deposition (PLD) in HF. In order to facilitate the electrochemical etching of the substrate, ethylene glycol electrolyte has been added to the solution and a thin metallic film of aluminium (Al) has been deposited onto a SiC prior to anodization. The structure and properties of the porous SiC layer formed by this method were investigated by Scanning Electron Microscopy (SEM) and Photoluminescence (PL). It shows that photoluminescence spectra exhibit two emission bands centered at 2.20 eV (blue band) and an extended broad band from 2.20 to 3.22 eV (green band) from porous 6H-SiC (PSC). On the contrary, porous thin 1.6 μm SiC layer exhibits only a blue band centered at 2.95 eV. Finally, the results indicate clearly that porous SiC gives off green and blue light. Also, there is a shift to blue luminescence with the same order of magnitude when using a thin SiC layer deposited onto silicon (p-Si(100)).

We theoretically studied current oscillations and the dynamics of the modulation-doped GaAs/AlGaAs heterostructure under the action of electric fields and a perpendicular magnetic field. The results show that the current oscillations and hysteresis in the system can be found under the DC bias voltage. Under the effect of the increasing magnetic fields, the oscillations will disappear and the width of the hysteresis is broader. Considering the AC part, the system shows interesting nonlinear behaviors like the route of an inverse period-doubling to chaos, quasiperiodicity, and frequency-locking.

We investigate the optical conductivity in the two-dimensional (2D) square and triangular tight-binding lattice-electron model with staggered magnetic flux (SMF). The SMF results in a two-sublattice system with two branches of energy bands in both cases, and even generates new flux-dependent optical properties. Results for the flux parameter dependence of the mean kinetic energy, the Drude weight and the optical conductivity are discussed in detail. A comparison between the two cases has been done.

Glasses of the xGd₂O₃ · (100-x)[4Bi₂O₃ · GeO₂] system, with 1 ≤ x ≤ 30 mol% were obtained and investigated by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The EPR spectra of the studied glasses reveal resonance sites with an unexpected high crystalline field in addition to the "U" spectrum, typical for Gd³⁺ ions in glasses. This absorption line is due to Gd³⁺ ions that replace Bi³⁺ ions from the host glass matrix and can play former role of the unconventional network in the studied glasses. EPR and magnetic susceptibility data show that for low Gd₂O₃ content, x ≤ 10 mol%, the Gd³⁺ ions are randomly distributed in the host glass matrix and are present only as isolated species. For higher Gd₂O₃ content, x > 10 mol%, the Gd³⁺ ions appear as both isolated and antiferromagnetically coupled species.

The thermomagnetic waves in conducting medium is theoretically studied. The frequencies of these waves are obtained. The amplitude and conditions of radiation by media are determined in the first approximation.