Scaling of transition temperature and CuO2 plane buckling in a high-temperature superconductor

A characteristic feature of the high-temperature superconductors is the existence of a chemical composition that gives a maximum transition temperature, Tc, separating the so-called under-doped and over-doped regimes1, 2. This behaviour is thought to be universal for high-temperature superconductors. In practice, there are only a few high- Tc compounds for which the composition can be varied continuously throughout the entire doping range. Here we report a study of correlations between structure and Tc in a compound with the ‘123’ structure in which both the under-doped and over-doped regimes can be accessed. We observe a clear scaling between Tc and the buckling of the copper oxide planes; both go through a maximum at the same oxygen composition (and hence doping level), so implying a common origin. Previous work has shown that, for a fixed chemical composition, increased CuO2 plane buckling lowers the transition temperature3,4,5,6,7,8,9,10,11. Thus the observation of a maximum in the buckling at the maximum Tc indicates that, as the composition is changed to increase Tc, there is a structural response that competes with superconductivity.