Electronic phase separation: Recent progress in the old problem

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