Model for the inverse isotope effect of FeAs-based superconductors in the π-phase-shifted pairing state

초록

The isotope effects for Fe-based superconductors are considered by including the phonon and magnetic fluctuations within the two-band Eliashberg theory. We show that the recently observed inverse isotope effects of Fe, alpha(Fe)approximate to-0.18 +/- 0.03 [P. M. Shirage, K. Kihou, K. Miyazawa, C.-H. Lee, H. Kito, H. Eisaki, Y. Tanaka, and A. Iyo, arXiv:0903.3515 (unpublished)] as well as the large positive isotope exponent (alpha approximate to 0.35) can naturally arise for the magnetically induced sign revered s-wave pairing state within reasonable parameter range. Either experimental report cannot be discarded from the present analysis based on the parameter values they require. The inverse and positive isotope effects mean, respectively, the interband and intraband dominant electron-phonon interactions. We first make our points based on the analytic result from the square-well potential model and present explicit numerical calculations of the two-band Eliashberg theory.

키워드