Europhys. Lett, 47 (5), pp. 588-594 (1999)
Anomalous impurity effects in nonadiabatic superconductors
M. Scattoni 1, C. Grimaldi 1,2 and L. Pietronero 1,2
1 Dipartimento di Fisica, Università di Roma I "La
Piazzale A. Moro, 2, 00185 Roma, Italy
2 Istituto Nazionale Fisica della Materia, Unità di Roma 1 - Roma, Italy
(received 26 March 1999; accepted 5 July 1999)
PACS. 71.38 - Polarons and electron-phonon interactions.
PACS. 74.20Mn - Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.).
PACS. 74.62Dh - Effects of crystal defects, doping and substitution.
We show that, in contrast with the usual electron-phonon Migdal-Eliashberg theory, the critical temperature of an isotropic s-wave nonadiabatic superconductor is strongly reduced by the presence of diluted nonmagnetic impurities. Our results suggest that the recently observed -suppression driven by disorder in K3C60 (Phys. Rev. B, 55 (1997) 3866) and in Nd2-xCexCuO (Phys. Rev. B, 58 (1998) 8800) could be explained in terms of a nonadiabatic electron-phonon coupling. Moreover, we predict that the isotope effect on has an impurity dependence qualitatively different from the one expected for anisotropic superconductors.
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