Phase separation, percolation and giant isotope effect in manganites

TL;DR

This paper reviews phase separation phenomena in strongly correlated electron systems, focusing on doped manganites, and discusses theoretical models, experimental observations, and the giant isotope effect related to phase coexistence and percolation.

Contribution

It provides a comprehensive theoretical and experimental analysis of phase separation and isotope effects in doped manganites, highlighting the percolative nature of their phase transitions.

Findings

Evidence of phase separation in manganites.

Construction of the phase diagram near critical doping levels.

Observation of a giant isotope effect in these systems.

Abstract

Phase separation and a tendency to form inhomogeneous structures seems to be a generic property of systems with strongly correlated electrons. After shortly summarising the existing theoretical results in this direction, I concentrate on the phenomena in doped manganites. I discuss general theoretical results on the phase separation at small doping and close to the doping x=0.5. The "global" phase diagram in this region is constructed. These general results are illustrated on the example of the particular system with rich and complicated properties - (LaPr)_(1-x)Ca_xMnO_3 in which there exist a ferromagnetic metallic (FM) phase and a charge ordered (CO) insulating one. The experimental situation in this system is discussed and the interpretation is given in the framework of the model with competition of FM and CO, and the indications of phase separation and percolative nature of this system are given. Giant isotope effect observed in this situation is shortly discussed.