Effect of density of state on isotope effect exponent of twoband superconductors.pdf

Effect of Density of state on Isotope Effect Exponent of Two- band Superconductors P.Udomsamuthirun(1),C.Kumvongsa (2) ,A.Burakorn(1), P.Changkanarth(1)and S.Yoksan(1) (1) Department of Physics, Faculty of Science, Srinakharinwirot University,Bangkok 10110,Thailand.E-mail: udomsamut55@ (2) Department of Basic Science, School of Science, The University of the Thai Chamber of Commerce, Dindaeng , Bangkok 10400, Thailand. Keywords: isotope effect exponent, two-band superconductors, Density of state PACS : 74.20.Fg, 74.70.Ad. Abstract The exact formula of T ’s equation and the isotope effect exponent of two- c band s-wave superconductors in weak-coupling limit are derived by considering the influence of two kinds of density of state : constant and van Hove singularity . The paring interaction in each band consisted of 2 parts : the electron-phonon interaction and non-electron-phonon interaction are included in our model. We find that the interband interaction of electron-phonon show more effect on isotope exponent than the intraband interaction and the isotope effect exponent with constant density of state can fit to experimental data,MgB and high-T superconductor, better than van Hove 2 c singularity density of state. 2 1.Introduction The isotope effect exponent, α, is one of the most interesting properties of superconductors. In the conventional BCS theory α 0 .5 for all element. In high-Tc superconductors , experimenter found that α is smaller than 0.5[1-3]. This unusual small value leads to suggestion that the pairing interaction might be predominantly of electronic origin with a possible small phononnic contribution[4]. To explain the unusual isotope effect in high-Tc