The Variation of Isotope Effect Coefficient a in Impure High Tc Superconductors
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Date
2005-07
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Addis Ababa University
Abstract
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.
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Keywords
AG-equation, Superconducting transition temperature Tc, Isotope effect coefficien, Impurity effect, Disorder (defect) effect