Theory of Ferromagnetic Metal to Paramagnetic Insulator Transition i in R_{1-x}A_{x}MnO_{3}

TL;DR

This paper develops a theoretical model for the transition from ferromagnetic metal to paramagnetic insulator in manganites, incorporating various interactions and disorder effects, and explains experimental observations of metal-insulator transitions.

Contribution

It introduces a comprehensive theoretical framework combining double-exchange, Coulomb, Jahn-Teller, and disorder effects to explain phase transitions in manganites.

Findings

Sharp increase in lattice distortion fluctuations near $T_c$

Spin and Jahn-Teller disorders induce MIT at low carrier density

Cation size mismatch disorder explains MIT in certain doping ranges

Abstract

The double-exchange model for the Mn oxides with orbital degeneracy is studied with including on-site Coulomb repulsion, Jahn-Teller (J-T) coupling and doping-induced disorder. In the strong interaction limit, it is mapped onto a single-band Anderson model, in which all scattering mechanisms can be treated on an equal footing. A sharp rise in the mean square fluctuation of lattice distortions is found near the Curie temperature $T_c$, in agreement with experiments. We show that the spin and J-T disorders lead to a metal-insulator transition (MIT) only at low carrier density. The MIT observed in samples with $0.2\leq x<0.5$ can be explained by further including the disorder effect of cation size mismatch.