A precise measurement of the oxygen isotope effect on the néel temperature in cuprates

A limiting factor in the ability to interpret isotope effect measurements in cuprates is the absence of sufficiently accurate data for the whole phase diagram; there is precise data for T c, but not for the antiferromagnetic transition temperature T N. Extreme sensitivity of T N to small changes in the amount of oxygen in the sample is the major problem. This problem is solved here by using the novel compound (Ca_0.1La_0.9)(Ba _1.65La_0.35) Cu₃ O_yfor which there is a region where T N is independent of oxygen doping. Meticulous measurements of T N for samples with 16_Oand 18_Ofind the absence of an oxygen isotope effect on T N with unprecedented accuracy. A possible interpretation of our finding and existing data is that isotope substitution affects the normal state charge carrier density.