Polaron framework to account for transport properties in metallic epitaxial manganite films

Abstract

We propose a model for the consistent interpretation of the transport behavior of manganese perovskites in both the metallic and insulating regimes. The concept of polarons as charge carriers in the metallic ferromagnetic phase of manganites also solves the conflict between transport models, which usually neglects polaron effects in the metallic phase, and, on the other hand, optical conductivity, angle-resolved spectroscopy, and neutron scattering measurements, which identify polarons in the metallic phase of manganites down to 6 K. Transport characterizations of epitaxial ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films in the thickness range of 5--40 nm and temperature interval of 25--410 K have been accurately collected. We show that taking into account polaron effects allows us to achieve an excellent fit of the transport curves in the whole temperature range. The current carriers density collapse picture accurately accounts for the properties variation across the metal-insulator transitions. The electron-phonon coupling parameter \ensuremath{\gamma} estimations are in a good agreement with theoretical predictions. The results promote a clear and straightforward quantitative description of the manganite films involved in charge transport device applications and promises to describe other oxide systems involving a metal-insulator transition.