  We performed high-resolution angle-resolved photoemission spectroscopy on
electron-doped high-Tc superconductor Pr0.89LaCe0.11CuO4 to study the
anisotropy of the superconducting gap. The observed momentum dependence is
basically consistent with the dx2-y2-wave symmetry, but obviously deviates from
the monotonic dx2-y2 gap function. The maximum gap is observed not at the zone
boundary, but at the hot spot where the antiferromagnetic spin fluctuation
strongly couples to the electrons on the Fermi surface. The present
experimental results unambiguously indicate the spin-mediated pairing mechanism
in electron-doped high-Tc superconductors.
