Oxygen isotope effects in high-quality thin films of manganites: Quantitative constraints on the physics of manganites

Abstract

Oxygen isotope effects on the transport properties have been studied in high-quality epitaxial thin films of La_{0.75}Ca_{0.25}MnO_{3} and Nd_{0.7}Sr_{0.3}MnO_{3}. In the paramagnetic state, the resistivity can be well fitted by ρ(T) = (A/\sqrt{T})\exp(E_ρ/k_{B}T) with the parameters A and E_{a} depending strongly on the oxygen isotope mass. The resistivity below 80 K almost perfectly follows ρ= ρ_{o}+ Bω_{s}/\sinh^{2}(\hbarω_{s}/2k_{B}T) with \hbarω_{s}/k_{B} \sim 100 K. Both ρ_{o} and B increase by about 15(3)% upon raplacing $^{16}$O by $^{18}$O. The results provide quantitative constraints on the basic physics of manganites.