An Origin of CMR: Competing Phases and Disorder-Induced Insulator-to-Metal Transition in Manganites

TL;DR

This paper presents a theoretical study on how competing phases and disorder induce an insulator-to-metal transition in manganites, shedding light on the colossal magnetoresistance phenomenon.

Contribution

It introduces a disorder-induced insulator-to-metal transition mechanism driven by phase competition, expanding understanding beyond existing theories.

Findings

Disorder destroys charge order, leading to metallic states.

Disorder enhances charge fluctuations above transition temperature.

The scenario explains colossal magnetoresistance through phase competition.

Abstract

We theoretically explore the mechanism of the colossal magnetoresistance in manganese oxides by explicitly taking into account the phase competition between the double-exchange ferromagnetism and the charge-ordered insulator. We find that quenched disorder causes a drastic change of the multicritical phase diagram by destroying the charge-ordered state selectively. As a result, there appears a nontrivial phenomenon of the disorder-induced insulator-to-metal transition in the multicritical regime. On the contrary, the disorder induces a highly-insulating state above the transition temperature where charge-ordering fluctuations are much enhanced. The contrasting effects provide an understanding of the mechanism of the colossal magnetoresistance. The obtained scenario is discussed in comparison with other theoretical proposals such as the polaron theory, the Anderson localization, the multicritical-fluctuation scenario, and the percolation scenario.