Uniform optimal plane charge order in superconducting cuprates

For simple overoxidized cuprates it was found that 1, scale universally with stoichiometric O- holes (h) per total 0 [cluster size or hole density]. Moreover, their T-c often optimize at a doping limit of formal plane Cu oxidation of 2.5+, corresponding formally to a uniform alternate hole charge order, denoted P2. In cases of complex selfdopings the stoichiometric holes are not known a priori. However, assuming that optimal T-c will generally correspond to a uniform charge order, their values should be predictable on the O- hole cluster model. Here we successfully apply this formalism to optimized complex cuprates that are based on M=Hg, Tl, Bi. In a rule of perplexing simplicity, satisfactory agreement with experiment is again obtained on the assumption of a uniform selfdoping to P2. The respective doping levels are reached through a combination of overoxidation and selfdoping [reductions of M]. This selfdoping is driven by lattice tension adjustment. The rare exceptional cases, where observed T-c are unusually high, can help in devising strategies for how to further increase T-c. These remarkable empirical rules point to an understanding that superconductivity reflects a charge order related phenomenon and can be manipulated by lattice pressure. (C) 2002 Elsevier Science B.V. All rights reserved.