Saddle-point van Hove singularity and the phase diagram of high-Tc cuprates

We examine the generic phase behavior of high-T-c cuprate superconductors in terms of a universal van Hove singularity in the strongly overdoped region. Using a dispersion derived from angle-resolved photoemission spectroscopy (ARPES), we solve the BCS gap equation and show that the pairing interaction or pairing energy cutoff must be a rapidly declining function of doping. This result is prejudicial to a phonon-based pairing interaction and more consistent with a magnetic or magnetically enhanced interaction.