Correlated polarons in dissimilar perovskite manganites - art. no. 174405

We report x-ray scattering studies of broad peaks located at (0.5 0 0)/(0 0 .5 0)-type wave vectors in the paramagnetic insulating phases of La0.7Ca0.3 MnO3 and Pr(0.)7Ca(0.3)MnO(3). We interpret the scattering in terms of corr elated polarons and measure isotropic correlation lengths of 1-2 lattice co nstants in both samples. Remarkably, the size of these correlated polarons remains constant over the entire temperature range investigated. In La0.7Ca 0.3MnO3, this range extends up to similar to 400 K. at which temperature th e peaks are observed to disappear. Based on the wavevector, the correlated polarons are found to be consistent with a CE-type structure. Differences i n behavior between the samples arise as they are cooled through their respe ctive transition temperatures and become ferromagnetic metallic (La0.7Ca0.3 MnO3) or charge and orbitally ordered insulating (Pr0.7Ca0.3MnO3). Since th e primary difference between the two samples is the trivalent cation size, these results illustrate the robust nature of the correlated polarons to va riations in the relative strength of the electron-phonon coupling, in contr ast to the sensitivity of the low-temperature ground state to such variatio ns.