Electronic transport by small polarons in La0.5Sr0.5MnO3

Electrical conductivity measurements on La0.5Sr0.5MnO3 (LSM5) thin films as a function of temperature are presented. These are used to demonstrate that the electronic transport in LSM5 is well described by the Emin-Holstein adiabatic small polaron model. Measurements have also been performed on bulk samples. Even if the conductivity behaves somewhat differently in the latter case, the same polaronic model still applies. The polaron densities extracted from conductivity measurements are very similar, ranging from 7 to 8x10(21) cm(-3) for thin films and are 9.1x10(21) cm(-3) for bulk samples. These results agree quite well with the nominal polaron density for LSM5, 8.4x10(21) cm(-3). We have also derived important quantities for transport in LSM5. For thin films, we obtained hopping energies, W-H, ranging between 73 and 99 meV and almost constant, at 34 meV, for bulk samples. By fitting conductivity measurements from 50 to 1123 K, we also find the zero point interaction constant, gamma (0), to be 0.35 in thin films. These conductivity results are compared with the literature. (C) 2001 American Institute of Physics.