Disorder-Driven Quantum Phase Transition from Antiferromagnetic Metal to Insulating State in Multilayered High-T_c Cuprate (Cu,C)Ba₂Ca₄Cu₅O_y

Abstract

We report on superconducting (SC) characteristics for the oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba₂Ca₄Cu₅O_y [Cu-1245(OPT)], which includes pyramidal outer planes (OPs) and square inner planes (IPs). As a result of a reduction in the carrier density, the superconductivity for Cu-1245(OPT) occurs at the nearly optimally doped OPs with T_c=98 K. The onset of static antiferromagnetic (AFM) order at IPs is evidenced from the observation of zero-field Cu NMR at low temperatures, although the SC transition at OPs emerges below T_c=98 K. A disorder, which is actually mapped onto the underdoped IPs, is demonstrated to cause a quantum phase transition from AFM metal to insulating state in an underdoped regime. This finding reinforces that an AFM metallic phase exists between the AFM insulating phase and the SC phase for the ideally flat CuO₂ plane without disorder, as reported for the IPs in optimally doped Hg-1245 with the same doping level as in Cu-1245(OPT).