Universal doping dependence of the ground-state staggered magnetization of cuprate superconductors

Using muon spin rotation we determine the zero-temperature staggered antiferromagnetic order parameter M-0 versus hole doping measured from optimum Delta p(m), in the (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy system. In this system the maximum T-c and the superexchange J vary by 30% between families (x). M-0(x,Delta p(m)) is found to be x independent. Using neutron diffraction we also determine the lattice parameters variations for all x and doping. The oxygen buckling angle is found to change with x, implying a change in the holes kinetic energy. We discuss the surprising insensitivity of M-0(x,Delta p(m)) to the kinetic-energy variations in the framework of the t-J model.