Polaronic excitations in CMR manganite films

TL;DR

This paper investigates polaronic excitations in manganite films using optical spectroscopy, revealing large polarons in LSMO and small polarons in LCMO, and discusses their implications for charge transport.

Contribution

It provides experimental evidence distinguishing large and small polarons in different manganite films through optical and transport measurements.

Findings

Large polaron excitations identified in LSMO.

Small polaron excitations identified in LCMO.

Distinct polaronic behaviors linked to different manganite compositions.

Abstract

In the colossal magnetoresistance manganites polarons have been proposed as the charge carrier state which localizes across the metal-insulator transition. The character of the polarons is still under debate. We present an assessment of measurements which identify polarons in the metallic state of La{2/3}Sr{1/3}MnO{3} (LSMO) and La{2/3}Ca{1/3}MnO{3} (LCMO) thin films. We focus on optical spectroscopy in these films which displays a pronounced resonance in the mid-infrared. The temperature dependent resonance has been previously assigned to polaron excitations. These polaronic resonances are qualitatively distinct in LSMO and LCMO and we discuss large and small polaron scenarios which have been proposed so far. There is evidence for a large polaron excitation in LSMO and small polarons in LCMO. These scenarios are examined with respect to further experimental probes, specifically charge carrier mobility (Hall-effect measurements) and high-temperature dc-resistivity.