Isotope effect on $m^{\ast }$ in high-T_c materials due to the breakdown of Migdal's theorem

Abstract

We show that the inclusion of effects beyond Migdal's limit in the electron-phonon interaction naturally leads to an isotope effect for the effective mass $m^{\ast }$ of the charge carriers even much before reaching the polaron limit. This is the situation already considered in our approach to nonadiabatic superconductivity. Such a result provides a scenario different from the polaronic one for the interpretation of the recently observed isotope effect on $m^{\ast }$ in YBa${}_2$Cu${}_3$O${}_{6+x}$ and La${}_{2-x}$Sr${}_x$CuO${}_4$.

6 pages, revtex (euromacr.tex,europhys.sty); 3 postscript figures

References in corpus (1)

• Dynamical mean-field theory of the small polaron

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