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

TL;DR

This study uses scanning tunneling spectroscopy to detect and map polaronic quasiparticle excitations across the insulator-metal transition in La0.7Ca0.3MnO3 films, revealing persistent polarons in both phases.

Contribution

It provides the first nanoscale spatial mapping of polaron signatures across the insulator-metal transition in manganite films.

Findings

Polaronic features are observed throughout the surface in both insulating and metallic phases.

Polaron-binding energies are spatially mapped and show widespread presence.

Polarons are not confined to insulating regions but are present in the metallic phase.

Abstract

In this work we map tunnel conductance curves with nanometric spatial resolution, tracking polaronic quasiparticle excitations when cooling across the insulator-to-metal transition in La0.7Ca0.3MnO3 films. 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.