Narrow Results

A three square well model is developed, which allows one to easily calculate the correlation between the coupling strength parameters and superconducting transition temperature (T_c), pressure and volume derivative of T_c and isotope effect exponent for MgB₂. Upon considering the three interactions, namely, electron-phonon, electron-plasmon and Coulomb, the analytical solutions for the energy gap equation allow us to understand the relative interplay of these interactions. The values of the coupling strength and of the Coulomb interaction parameter indicate that the superconductor is in the intermediate coupling regime. The superconducting transition temperature of MgB₂ for the 2D band is estimated as 41 K for and μ^σ*≈0.28. We present correlation curves of T_c with various coupling strengths as electron-phonon , electron-plasmon and the Coulomb screening parameter (μ^σ*). The present approach also explains the reported boron isotope effect and the pressure derivative of T_c in the test material. We suggest from these results that both the plasmons and phonons within the framework of a three square well scheme consistently explain the effective electron-electron interaction leading to superconductivity in MgB₂. The implications of the effective interactive potential with both σ and π carriers and its analysis are discussed.

The properties of long wavelength optical phonons in mixed crystals AB_1-xC_x is discussed by a model similar to Modified Random Element Isodisplacement (MREI). Using this method we investigate the frequencies, the dielectric functions, and the reflectivity of several mixed crystals. It is found that this model can be applied to the one-mode behavior, the two-mode behavior, and that of the third category. So the model provides a possible way to understand the optical character of the ternary mixed crystal. Based on it, we can discuss other problems similar to electron–phonon interaction and so on.

The results of an ensemble Monte Carlo simulation of the steady-state electron drift velocity as a function of applied electric field in Al_0.2Ga_0.8N are presented. The effect of various material parameters on the calculated velocity is assessed by varying each parameter independently by ± 30%. It is found that both the optical phonon energy and intervalley separation energy alter the peak electron velocity. Variations in the dielectric constants and central valley effective mass have more effect upon the peak drift velocity and act to alter the threshold electric field. The combined effects of a greater central valley effective mass and a larger phonon energy in Al_0.2Ga_0.8N result in a greater threshold field.

We present a comprehensive study of the transport dynamics of electrons in the binary and ternary compounds AlN, GaN and Al_0.2Ga_0.8N. Calculations are made using a non-parabolic effective mass energy band model, Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models. The effects of alloy scattering on the electron transport physics are examined. The steady-state velocity field curves and low field mobilities are calculated at room temperature. The results are in fair agreement with other recent calculations.

Upon considering the three interactions namely, the electron–acoustic phonon, the electron–optical phonon and the Coulomb, the analytical solutions for the energy gap equation allows one to determine the electronic structure parameters to discuss the behavior of superconducting transition temperature (T_c) and isotope effect coefficient (α) for layered structure YNi₂ B₂C. T_c of 17 K is estimated for YNi₂B₂C with electron–acoustic phonon (λ_ac) = 0.31, electron–optical phonon (λ_op) = 0.1 and Coulomb screening parameter (μ*) = 0.126 indicating that the YNi₂B₂C superconductor is in the intermediate coupling regime. To correlate the T_c with various coupling strengths as λ_ac, λ_op and μ*, we present curves of T_c with them. The present approach also explains the conditions for the Boron and Carbon isotope effect. The negative pressure coefficient of T_c in this layered material is attributed to the contraction along c-axis under hydrostatic pressure. We suggest from these results that both the acoustic and optical phonons within the framework of a three-square well scheme consistently explains the effective electron–electron interaction leading to superconductivity in layered structure YNi₂B₂C.

An analytical treatment based on the hydrodynamic model of plasmas is developed to study parametric amplification and oscillation of optical phonon modes in weakly polar narrow direct-gap magnetized semiconductor plasmas. Second-order optical susceptibility arising due to nonlinear polarization and the basic operational characteristics of the parametric device, viz. threshold nature, power gain mechanisms and conversion efficiency, are obtained. The effects of doping, magnetic field and excitation intensity, on the above operational characteristics have been studied in detail. Numerical estimates are made for an n-InSb crystal at 5 K duly irradiated by a pulsed 10.6 $\mu \mathrm{\text{m}}$ CO₂ laser. The analysis suggests the possibility of observing super-fluorescent parametric emission and oscillation in moderately doped n-InSb crystal under off-resonant nanosecond pulsed not-too-high power laser irradiation, the crystal being immersed in a large magnetic field.

CdSe semiconducting nanoparticles in the range of 6–7 nm in size were synthesized by a soft chemical procedure at room temperature. The particles were characterized by powder X-ray diffraction, UV–visible optical spectroscopy revealing nanocrystallization, and quantum mechanical electron confinement. Photoluminescence and Raman spectroscopy of these nanocrystalline powders indicated optical phonon confinement. Asymmetric line shapes revealed occurrence of nonzone center phonons. The particles could be successfully deposited on ITO substrate by electrophoresis to obtain self-organized quantum dot array. Scanning electron microscopy, high-resolution scanning electron microscopy, confocal fluorescence microscopy, and atomic force microscopy investigations revealed self-similar deposits.