We discuss the nature of electron-lattice interaction in optimally doped Bi2Sr2CaCu2O8+δ samples, using isotope effect (IE) in angle resolved photoemission spectroscopy (ARPES) data. The IE in the ARPES line width and the IE in the ARPES dispersion are both quite large, implying a strong electron-lattice correlation. The strength of the electron-lattice interaction is ``intermediate,'' i.e. stronger than the Migdal-Eliashberg regime but weaker than the small polaron regime, requiring a more general picture of the ARPES ``kink'' than the commonly used Migdal-Eliashberg picture. The two IEs also imply a complex interaction, due to their strong momentum dependence and their differing sign behaviors. In sum, we propose an intermediate-strength coupling of electrons to localized lattice vibrations via charge density fluctuations.
@article{arxiv.cond-mat/0701291,
title = {Strong and complex electron-lattice correlation in optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$},
author = {G. -H. Gweon and S. Y. Zhou and M. C. Watson and T. Sasagawa and H. Takagi and A. Lanzara},
journal= {arXiv preprint arXiv:cond-mat/0701291},
year = {2007}
}