Intertwined evolution of superconductivity and pseudogap in the presence of strong mode coupling

A commonly perceived salient feature of the otherwise extremely complex electronic phase diagram in cuprate high temperature ($T_c$) superconductors is the appearance of relatively simple superconductivity in the deeply overdoped regime. In a recent measurement of superfluid density only a small fraction of carriers are found to participate in the superconductivity in this region, violating a simple fermionic description. Here we report systematic angle-resolved photoemission spectroscopy (ARPES) study that provides a complementary fermionic perspective. Increasing the doping through a narrow range in the overdoped regime, the single particle spectrum divorces itself from a pseudogap-infected uncanonical behavior, characterized by a large gap-$T_c$ ratio and non-BCS temperature dependence, to the canonical \textit{d}-wave BCS superconducting gap over the entire Fermi surface. Accompanying this evolution, an electron-phonon coupling (EPC) feature, modified by the pseudogap, also abruptly disappears in an equally narrow doping range, suggesting its potential role as the superconductivity 'enhancer' near the optimal $T_c$. A combined perspective of the complementary bosonic and fermionic picture is needed to fully describe the phase diagram.