Polaronic signature in the metallic phase of La0.7Ca0.3MnO3 films detected by scanning tunneling spectroscopy

In this work we map tunnel conductance curves with nanometric spatial resolution, tracking polaronic quasiparticle excitations when a La0.7Ca0.3MnO3 film is cooled across the insulator-to-metal transition. In the insulating phase the spectral signature of polarons, a depletion of conductance at low bias flanked by peaks, is detected all over the scanned surface. These features are still observed at the transition and persist on cooling into the metallic phase. Polaron-binding-energy maps reveal that polarons are not confined to regions embedded in a highly conducting matrix but are present over the whole field of view both above and below the transition temperature.