Theoretical study of superconducting state parameters of binary metallic glasses by a pseudopotential method

The theoretical investigations of the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ¹, transition temperature T_C, isotope effect exponent α and effective interaction strength N₀V of binary metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that λ and T_C are quite sensitive to the selection of the local field correction functions in comparisons with μ¹, α and N₀V. The T_C obtained from H-local field correction function is found in qualitative agreement with available experimental data and show linear nature with the concentration (C). A linear T_C equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other results for the experimental data. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the metallic glasses.     

Pressure dependence of the superconducting state parameters of a binary Ca<Subscript>70</Subscript>Mg<Subscript>30</Subscript> metallic glass superconductor

Theoretical computation of the pressure dependence of superconducting state parameters of a binary Ca₇₀Mg₃₀ metallic glass has been performed using the model potential formalism. Explicit expressions have been derived for the volume dependence of the electron-phonon coupling strength λ and the Coulomb pseudopotential μ*, considering the variation of the Fermi momentum k _F and Debye temperature θ_D with volume. Well-known Ashcroft’s empty core model pseudopotential and five different types of the local-field correction functions, namely, Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. have been used for obtaining pressure dependence of transition temperature T _C and the logarithmic volume derivative Φ of the effective interaction strength N ₀ V for the metallic glass superconductor. It has been obtained that T _C of Ca₇₀Mg₃₀ metallic glass decreases rapidly with increasing pressure up to 60% decrease in the volume, for which the μ* and Φ curves show a linear nature. The superconducting phase disappears at about 60% decrease in the volume.     

The spectral measurement of a high repetition rate tunable dye laser output using Fabry–Perot fringe

We present the measurement of spectral distribution of a high repetition rate dye laser by deriving explicit relationship of the parameters with ring diameter of the Fabry–Perot fringe pattern. The output characteristics and its variation has been represented by generating a composite picture of a single line scan across the ring diameter of the Fabry–Perot fringe, captured through CCD camera and frame grabber card.     

Water Vapor Enhancement of Rates of Peroxy Radical Reactions

Peroxy radicals can complex with water vapor. These complexes affect tropospheric chemistry. In this study, β‐HEP (hydroxyethyl peroxy radical) serves as a model system for investigating the effect of water vapor on the kinetics and product branching ratio of the self‐reaction of peroxy radicals. The self‐reaction rate coefficient was determined at 274–296 K with water vapor between 1.0 × 10¹⁵ and 2.5 × 10¹⁷ molecules cm^?3 at 200 Torr total pressure by slow‐flow laser flash photolysis coupled with UV time‐resolved spectroscopy and long‐path, wavelength modulated, diode‐laser spectroscopy. The overall self‐reaction rate constant expressed as the product of both a temperature‐dependent and water vapor–dependent term is , suggesting formation of a β‐HEP‐H₂O complex is responsible for the increase in the self‐reaction rate coefficient with increasing water concentration. Complex formation is supported by computational results identifying three local energy minima for the β‐HEP‐H₂O complex. As the troposphere continues to get warmer and wetter, more of the peroxy radicals present will be complexed with water. Investigating the effect of water vapor on kinetics of atmospherically relevant radicals and determining the effects of these altered kinetics on tropospheric ozone concentrations is thus important.     

Superconducting state parameters of binary alloys

The theoretical investigation of the superconducting state parameters (SSP) viz. electron–phonon coupling strength $\lambda$, Coulomb pseudopotential μ^*, transition temperature T_C, isotope effect exponent α and effective interaction strength N_OV of large numbers of binary alloys have been made extensively in the present work using a model potential formalism for the first time with pseudo-atom-alloy (PAA) model. A considerable influence of various exchange and correlation functions on $\lambda$ and μ^* is found from the present study. The present results of the SSP are found in qualitative agreement with the available experimental data wherever exist.     

Intercalation and anisotropy of optical absorption in MoRe0.005Se1.995 single crystals

The optical energy gap of MoRe_0.005Se_1.995 single crystal has been measured at room temperature near the fundamental absorption method. The incident light was polarized along c‐axis of the crystals. Two and three dimensional models are adopted for generating the results. Direct as well as indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The three dimensional model could be used to describe the optical properties of the single crystal of MoRe_0.005Se_1.995. Also, the optical energy gaps depend upon the amount of the intercalating Re material, which show the anisotropy of the chemical bonds. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of optical absorption in layered single crystals

The optical energy gap of Re doped MoSe₂ single crystal Mo_0.995Re_0.005Se₂ has been measured at room temperature near the fundamental absorption edge. The incident light was kept normal to the basal plane i.e. along the c‐axis of the grown crystals. Results have been given on the basis of two and three dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The three dimensional model and not the two dimensional could be used to describe the optical properties of Re doped MoSe₂ single crystal. Also, the optical energy gaps depend upon the amount of the intercalating Re material. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of the optical absorption in layered single crystals of MoRe0.001Se1.999

Energy gap of MoRe_0.001Se_1.999 single crystal has been determined by fundamental absorption methods. The incident light was polarized along c‐axis of the crystals. The interpretion of the data is given within frameworks of two and three dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons participating in the process. The three dimensional model could be used to describe the optical properties of the single crystal. The energy gaps depend upon the amount of the intercalating Re material, which show the anisotropy of the chemical bonds. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phonon dynamics of glassy copper alloys

The well recognized model potential is used to investigate the phonon properties for five glassy Copper alloys viz. Cu₅₇Zr₄₃, Cu₆₀W₄₀, Cu₃₃Y₆₇, Cu₄₃Ti₅₇ and Cu₆₆Ti₃₄. The thermodynamic and elastic properties are also computed from the elastic limits of the phonon dispersion curves (PDC). Three theoretical approaches given by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS) are used in the present study to compute the PDC. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are employed to see the effect of exchange and correlation in the aforesaid properties.