  The origin of a ubiquitous bosonic coupling feature in the photoemission
spectra of high-Tc cuprates, an energy-momentum dispersion 'kink' observed at
~70 meV binding energy, remains a two-decade-old mystery. Understanding this
phenomenon requires an accurate description of the coupling between the
electron and some collective modes. We report here ab initio calculations based
on GW perturbation theory and show that correlation-enhanced electron-phonon
interaction in cuprates gives rise to the strong kinks, which not only explains
quantitatively the observations but provides new understanding of experiments.
Our results reveal it is the electron density-of-states being the predominant
factor in determining the doping-dependence of the kink size, manifesting the
multi-band nature of the cuprates, as opposed to the prevalent belief of it
being a measure of the mode-coupling strength.
