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 𝑇𝑐, but not for the antiferromagnetic transition temperature 𝑇𝑁. Extreme sensitivity of 𝑇𝑁 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 (Ca0.1La0.9)(Ba1.65La0.35)Cu3O𝑦 for which there is a region where 𝑇𝑁 is independent of oxygen doping. Meticulous measurements of 𝑇𝑁 for samples with 16O and 18O find the absence of an oxygen isotope effect on 𝑇𝑁 with unprecedented accuracy. A possible interpretation of our finding and existing data is that isotope substitution affects the normal state charge carrier density.