Electronic phase separation: recent progress in the old problem

TL;DR

This review discusses recent progress in understanding nanoscale electronic phase separation in strongly correlated materials, highlighting the formation of ferromagnetic droplets, effects like colossal magnetoresistance, and the role of Fermi surface nesting.

Contribution

It provides a comprehensive overview of the mechanisms, types, and effects of electronic phase separation in various complex magnetic oxides and related systems.

Findings

Nanoscale ferromagnetic droplets form in antiferromagnetic and insulating matrices.

Electronic phase separation influences colossal magnetoresistance phenomena.

Systems with imperfect Fermi surface nesting exhibit unique phase separation behaviors.

Abstract

We consider the nanoscale electronic phase separation in a wide class of different materials, mostly in strongly correlated electron systems. The phase separation turns out to be quite ubiquitous manifesting itself in different situations, where the itineracy of charge carriers competes with their tendency toward localization. The latter is often related to some specific type of magnetic ordering, e.g. antiferromagnetic in manganites and low-spin states in cobaltites. The interplay between the localization-induced lowering of potential energy and metallicity (which provides the gain in the kinetic energy) favors an inhomogeneous ground state such as nanoscale ferromagnetic droplets in an antiferromagnetic insulating background. The present review article deals with the advances in the subject of electronic phase separation and formation of different types of nanoscale ferromagnetic (FM) metallic droplets (FM polarons or ferrons) in antiferromagnetically ordered (AFM), charge-ordered (CO), or orbitally-ordered (OO) insulating matrices, as well as the colossal magnetoresistance (CMR) effect and tunneling electron transport in the nonmetallic phase-separated state of complex magnetic oxides. It also touches upon the compounds with spin-state transitions, inhomogeneous phase-separated state in strongly correlated multiband systems, and electron polaron effect. A special, attention is paid to the systems with the imperfect Fermi surface nesting such as chromium alloys, iron-based pnictides, and AA stacked graphene bilayers.