  We report that the doping and temperature dependence of photoemission spectra
near the Brillouin zone boundary of Bi2Sr2CaCu2O8+delta exhibit unexpected
sensitivity to the superfluid density. In the superconducting state, the
photoemission peak intensity as a function of doping scales with the superfluid
density and the condensation energy. As a function of temperature, the peak
intensity shows an abrupt behavior near the superconducting phase transition
temperature where phase coherence sets in, rather than near the temperature
where the gap opens. This anomalous manifestation of collective effects in
single-particle spectroscopy raises important questions concerning the
mechanism of high-temperature superconductivity.
