Superconducting domes, ubiquitous across a variety of quantum materials, are often understood as a favored window for pairing opened by fluctuations of competing orders. Yet, a quantitative understanding of how such a window closes remains lacking. Using inelastic neutron scattering, we show that the superconducting dome in electron-doped SrTiO3-x results from the increase in the density of states and the inevitable collapse of the dipolar correlation length — both induced by doping.
