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.

我们考虑了多种不同材料中的纳米级电子相分离，主要是在高度相关的电子系统中。事实证明，相分离非常普遍地出现在不同的情况下，在这种情况下，电荷载流子的巡回运动与它们的局部化趋势竞争。后者通常与某种特定类型的磁有序有关，例如锰矿中的反铁磁和钴矿中的低自旋态。局部化引起的势能降低和金属性（这提供了动能的增加）之间的相互作用有利于非均匀的基态，例如反铁磁绝缘背景中的纳米级铁磁滴。本综述文章涉及电子相分离和反铁磁有序（AFM），电荷有序（CO）或轨道形成的不同类型的纳米级铁磁性（FM）金属液滴（FM极化子或铁）的研究进展。有序（OO）绝缘矩阵，以及在复杂磁性氧化物的非金属相分离状态下的巨大磁阻（CMR）效应和隧穿电子传输。它还涉及具有自旋态跃迁，强相关多带系统中非均匀相分离态以及电子极化子效应的化合物。特别要注意的是具有不完善的费米表面嵌套的系统，例如铬合金，铁基杀虫剂和AA堆叠的石墨烯双层。