Recent laser angle-resolved photoemission spectroscopy studies have established the presence of a new kink in the low-energy nodal dispersion of Bi2Sr2CaCu2O+8+δ (Bi-2212). The energy scale (~8-15 meV) of this kink appears below the maximum of the superconducting gap δ0. Therefore it is difficult to interpret this feature in terms of the usual coupling to a sharp dispersionless mode. In this paper we examine electron-phonon coupling to the in-plane acoustic phonon branch arising from the modulation of the screened Coulomb potential. We demonstrate that such a coupling has a strong forward scattering peak, and as a consequence, a kink occurs in the dispersion at an energy scale shifted by the local gap δ(k). In addition, considerations for the reduction of screening with underdoping naturally explains the observed doping dependence of the low-energy kink. These results point to a strong coupling to the acoustic branch which is peaked in the forward scattering direction and has important implications for transport and pairing in the high-Tc cuprates.
@article{arxiv.1101.1302,
title = {Evidence for forward scattering and coupling to acoustic phonon modes in high-T$_c$ cuprate superconductors},
author = {S. Johnston and I. M. Vishik and W. S. Lee and F. Schmitt and S. Uchida and K. Fujita and S. Ishida and N. Nagaosa and Z. X. Shen and T. P. Devereaux},
journal= {arXiv preprint arXiv:1101.1302},
year = {2012}
}