Photo-induced phase separation effect in cuprates

Moskvin, A. S.

doi:10.1088/1742-6596/21/1/017

Cited by 2 publications

(1 citation statement)

References 7 publications

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“…Our scenario can readily explain photo-induced effects in pseudo-impurity phase. 34 Indeed, the illumination of a material with light leads to the generation of eh-pairs that will proliferate and grow up to be a novel nonequilibrium EH droplet or simply to be trapped in either EH droplet with the rise in its volume fraction. The excitation energy appears to be lower when exciton is closer to the EH droplet.…”

Section: Nucleation Of Eh Droplets and Phase Separation Effects In Ct...mentioning

confidence: 99%

Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron–hole Bose liquid

Moskvin

2007

Low Temperature Physics

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We develop 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 M 0,± described in frames of S = 1 pseudo-spin (isospin) formalism by an effective anisotropic non-Heisenberg Hamiltonian which includes two types of single particle correlated hopping and the two-particle hopping. We show that the coherent states provide the optimal way both to a correct mean-field approximation and respective continuous models to describe the pseudo-spin system. Simple uniform mean-field phases include an insulating monovalent M 0 -phase, mixed-valence binary (disproportionated) M ± -phase, and mixed-valence ternary ("underdisproportionated") M 0,± -phase. We consider two first phases in more details focusing on the problem of electron/hole states and different types of excitons in M 0 -phase and formation of electronhole Bose liquid in M ± -phase. Pseudo-spin 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 M 0 -phase may be 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 and manganites that implies their instability with regard to the self-trapping of charge transfer excitons and the formation of electron-hole Bose liquid.

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Section: Nucleation Of Eh Droplets and Phase Separation Effects In Ct...mentioning

confidence: 99%

Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron–hole Bose liquid

Moskvin

2007

Low Temperature Physics

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Charge transfer transitions in multiferroicBiFeO3and related ferrite insulators

Moskvin²,

et al. 2009

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The optical response of the technologically interesting multiferroic BiFeO3 and related complex iron oxides, having high Néel or Curie temperature, is studied in the wide spectral range from 0.6 up to 5.8 eV by means of spectroscopic ellipsometry. The investigated iron oxides have different crystal symmetry with FeO6 octa hedral and FeO4 tetrahedral centers distorted to a certain degree. One of the two groups of materials includes BiFeO3, ErFeO3, Y.95Bi.05FeO3, oe-Fe2O3, Fe2-xGaxO3, and Fe3BO6 in which iron Fe3+ ions occupy only octahedral centrosymmetric or noncentrosymmetric positions and distortions range of 1-20 %. The second group includes LiFe5O8, BaFe12Ow, Sm3Fe5O12, and Ca2Fe2O5 in which Fe3+ ions occupy both octahedral and tetrahedral positions with a rising tetra/ortho ratio. We show that in the spectral range up to ~3.7 eV, the optical response is dominated by p-d charge transfer (CT) transitions, while at E > 3.7 eV both p-d and d-d CT transitions are revealed. At variance with several previous investigations, we present a correct and unified assignment of different dipole-allowed and dipole-forbidden CT transitions. All the ferrites investigated are CT insulators with the band gap determined by a dipole-forbidden p-d CT transition t1g ^ t2g, forming a ~2.5 eV band on the tail of a strong 3.0 eV band assigned to dipole-allowed p-d CT transitions t2u(w) ^ t2g in octahe dral FeOg centers. A noticeable enhancement of the optical response in BiFeO3 at ~4 eV as compared with other related iron oxides is attributed to CT transitions within the Bi-O bonds. We report an observation of unexpected midinfrared CT bands in calcium ferrite Ca2Fe2O5 and an enhanced structureless spectral weight in a wide range below the main CT bands in BiFeO3 with a remarkable smearing of the fundamental absorption edge. All these anomalies are assigned to CT instabilities accompanied by a self-trapping of p-d CT excitons and nucleation of electron-hole droplets. The optical detection of this CT instability agrees with the observation of a metal-insulator transition in bismuth ferrite.

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Photo-induced phase separation effect in cuprates

Cited by 2 publications

References 7 publications

Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron–hole Bose liquid

Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron–hole Bose liquid

Charge transfer transitions in multiferroicBiFeO3and related ferrite insulators

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