  Electronic band dispersions in copper oxide superconductors have kinks around
70 meV that are typically attributed to coupling of electrons to a bosonic
mode. We performed angle resolved photoemission spectroscopy (ARPES)
experiments on overdoped cuprate high temperature superconductors to test the
relationship between the superconducting transition temperature and
electron-bosonic mode coupling. Remarkably, the kinks remain strong in the
heavily overdoped region of the doping phase diagram of LSCO, even when the
superconductivity completely disappears. This unexpected observation is
incompatible with the conventional picture of superconductivity mediated by the
sharp bosonic modes that are responsible for the kink. Therefore, the pairing
likely originates from something else, such as from interactions with a very
broad electronic spectrum or from an unconventional mechanism without pairing
glue.
