  Angle resolved photoemission spectroscopy (ARPES) and resistivity
measurements are used to explore the overdoped region of the high temperature
superconductor Bi2Sr2CaCu2O8+delta. We find evidence for a new crossover line
in the phase diagram between a coherent metal phase for lower temperatures and
higher doping, and an incoherent metal phase for higher temperatures and lower
doping. The former is characterized by two well-defined spectral peaks in ARPES
due to coherent bilayer splitting and superlinear behavior in the resistivity,
whereas the latter is characterized by a single broad spectral feature in ARPES
and a linear temperature dependence of the resistivity.
