Optical Evidence for Mixed Phase Behavior in Manganites

TL;DR

This study uses synchrotron infrared measurements to investigate the phase behavior in manganites, revealing local distortions and insulating regions that coexist with metallic phases below transition temperatures.

Contribution

It provides optical evidence for the coexistence of insulating and metallic phases in manganites, highlighting local distortions affecting charge carrier dynamics.

Findings

Local distortions exist below TMI and TC, trapping conduction electrons.

Insulating phase persists at temperatures below transition points.

Resistivity drops are linked to magnetic ordering and reduction of insulating regions.

Abstract

Synchrotron infrared measurements were conducted over the range 100 to 8000 cm-1 on a self-doped LaxMnO3-d (x~~0.8) film. From these measurements we determined the conductivity, the effective number of free carriers, and the specific phonon modes as a function of frequency. While the metal-insulator transition temperature (TMI) and the magnetic ordering temperature (TC) approximately coincide, the free carrier density onset occurs at a significantly lower temperature (~~45 K below). This suggests that local distortions exist below TMI and TC which trap the eg conduction electrons. These regions with local distortions constitute an insulating phase which persists for temperatures significantly below TMI and TC. The initial large drop in resistivity is due to the enhanced magnetic ordering while further drops correspond to reductions in the insulating phase which increase the number of free carriers.