Phase diagram of high-Tc superconductor: Cu-NMR studies on multi-layered cuprates

Abstract A new phase diagram is presented for an ideally flat CuO 2 plane through the Cu-NMR studies on five-layered cuprates MBa 2 Ca 4 Cu 5 O y (M-1245) ( M = Hg , Tl , Cu ) , which includes an antiferromagnetic (AFM) metal phase and a uniform mixing phase of AFM metal and high- T c superconductivity (HTSC) in an under-doped region. It has been found that a disorder causes a quantum-phase transition from an AFM metal to an insulating state in an under-doped regime in the Cu-1245 where a disorder is introduced via an oxygen-reduced process. This finding reinforces that an AFM metallic phase exists between the AFM insulating phase and the SC phase for the ideally flat CuO 2 plane provided that a disorder is absent.