Abstract. A proper understanding of the mechanism for cuprate superconductivity can emerge only by comparing materials in which physical parameters vary one at a time. Here, we present a variety of bulk, resonance and scattering measurements on the (Ca_xLa_1−x) (Ba_1.75−xLa_0.25+x) Cu₃O_y high temperature superconductors, in which this can be done. We determine the superconducting, Néel, glass and pseudopage critical temperatures. In addition, we clarify which physical parameter varies, and, equally important, which does not, with each chemical modification. This allows us to demonstrate that a single energy scale, set by the superexchange interaction J, controls all the critical temperatures of the system. J, in turn, is determined by the in plane Cu–O–Cu buckling angle.

Received 27 December 2008
Published 30 June 2009