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

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 rho (T) = (A/sqrt{T})exp(E_{rho}/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 rho = rho_{o}+ Bomega_{s}/sinh^{2}(hbaromega_{s}/2k_{B}T) with hbaromega_{s}/k_{B} sim 100 K. Both rho_{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.