Browsing by Author "Demelash, Kassa"

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    The Variation of Isotope Effect Coefficient a in Impure High Tc Superconductors
    (Addis Ababa University, 2005-07) Demelash, Kassa
    The value of the critical temperature Te and isotope coefficient 0: could be greatly affected by a number of factors. Among them are the presence of magnetic impurities, non-magnetic impurities, disorder and defects. Following previous calculation of the critical temperature and isotope eflect by Singh and Kishore (P. Singh and R. Kishore, J. Supercond. 8, 9 (1995)), Singh et al. (S. P. Singh, R. K. Pandey, and P. Singh, J. Supercond. 9, 277 (1996)), Openov (Phys. Rev. B 58, 9468 (1998)) and Openov et al. (Phys. Rev. B 64,12513 (2001)) we have considered the effect of disorder (defect) on the superconducting transition temperature Te and isotope coefficient 0: with in the BCS model. An expression for Te and 0: as a function of potential and spin-flip scattering rates is derived by means of Green's functions technique. This is done with the introduction of the matrix Green function in the Nambu representation. The expression for In (i:) and C;J is obtained for a superconductor with an arbitrary degree of anisotropy of the superconducting order parameter, ranging from isotropic s-wave to d-wave and including anisotropic s-wave and mixed (s+d)-wave as particular cases. The universal dependence of (i:) on 'P (a factor proportional to ~, where T is the total relaxation time) and (:.) on Ii or 'P for a given value of X (a coefficient for anisotropy of the order parameter) is shown in different plots for different cases Key words: AG-equation, Superconducting transition temperature Te, Isotope effect coefficient, Impurity effect, Disorder (defect) effect.