  We report a genuine phase diagram for a disorder-free CuO_2 plane based on
the precise evaluation of the local hole density (N_h) by site-selective Cu-NMR
studies on five-layered high-Tc cuprates. It has been unraveled that (1) the
antiferromagnetic metallic state (AFMM) is robust up to N_h=0.17, (2) the
uniformly mixed phase of superconductivity (SC) and AFMM is realized at N_h<
0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM(Paramagnetism)
phases may be present at N_h=0.15 and T=75 K, (4) Tc is maximum close to a
quantum critical point (QCP) at which the AFM order collapses, suggesting the
intimate relationship between the high-Tc SC and the AFM order. The results
presented here strongly suggest that the AFM interaction plays the vital role
as the glue for the Cooper pairs, which will lead us to a genuine understanding
of why the Tc of cuprate superconductors is so high.
