We present a model approach to describe charge fluctuations and different charge phases in strongly correlated 3d oxides. As a generic model system one considers that of centers each with three possible valence states <$E M sup {0, symbol С}> described in frames of S = 1 pseudospin (isospin) formalism by an effective anisotropic non-Heisenberg Hamiltonian which includes both two types of single particle correlated hopping and the two-particle hopping. Simple uniform mean-field phases include an insulating monovalent <$E M sup 0> phase, mixed-valence binary (disproportionated) <$E M sup symbol С> phase, and mixed-valence ternary ("under-disproportionated") <$E M sup {0, symbol С}> phase. We consider two first phases in more details focusing on the problem of electron-hole states and different types of excitons in <$E M sup 0> phase and formation of electron-hole Bose liquid in <$E M sup symbol С> phase. Pseudospin formalism provides a useful framework for revealing and describing different topological charge fluctuations, in particular, like domain walls or bubble domains in antiferromagnets. Electron-lattice polarization effects are shown to be crucial for the stabilization of either phase. All the insulating systems such as <$E M sup 0> phase are subdivided to two classes: stable and unstable ones with regard to the formation of self-trapped charge transfer (CT) excitons. The latter systems appear to be unstable with regard to the formation of CT exciton clusters, or droplets of the electron-hole Bose liquid. The model approach suggested is believed to be applied to describe a physics of strongly correlated oxides

such as cuprates, manganites, bismuthates, and other systems with charge transfer excitonic instability and/or mixed valence. We shortly discuss an unconventional scenario of the essential physics of cuprates which implies their instability with regard to the self-trapping of charge transfer excitons and the formation of electron-hole Bose liquid.

Індекс рубрикатора НБУВ: В368.313 + В377.1

Рубрики:

Магнітні властивості надпровідників

Електричні властивості твердих тіл

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

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