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Failure of the Migdal-Eliashberg Theory of Superconductivity in Rb_3C_60

C. Grimaldi·E. Cappelluti·L. Pietronero·S. Straessler
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Abstract

We discuss the compatibility of the most accurate experimental data with the ordinary Migdal-Eliashberg theory of superconductivity in the fullerene compound Rb_3C_60. By using different model phonon spectra we conclude that the experimental data can be fitted only by invoking an electron-phonon coupling of order λ\simeq 3. This exceedingly high value is unphysical and it is not consistent with the basic assumptions of the Migdal-Eliashberg theory. On the contrary, by relaxing the adiabatic hypothesis on which the Migdal-Eliashberg theory rests, the experimental data can be fitted by much more realistic values of λ. This generalized theory predicts also characteristic features absent in the Migdal-Eliashberg framework which can be experimentally tested.

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C. Grimaldi, E. Cappelluti, L. Pietronero, S. Straessler. 2000-06-26. Failure of the Migdal-Eliashberg Theory of Superconductivity in Rb_3C_60. https://doi.org/10.1142/s0217979200003150

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