Raman Light Scattering in Pseudospin-Electron Model at Strong Pseudospin-Electron Interaction

Mysakovych,; Stasyuk,

doi:10.5488/cmp.7.2.347

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“…In Refs. [40][41][42], the contributions into Raman scattering intensity, connected with the mentioned collective pseudospin excitations (that correspond to the phonon-like vibrations of anharmonic subsystems in the YBaCuO structures) and electron intraband and interband transitions, were considered.…”

Section: (The Quantum Monte-carlo Calculations)mentioning

confidence: 99%

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Phase Transitions in the Pseudospin-Electron Model

Stasyuk

2007

Order, Disorder and Criticality

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November 18, 2018 21:48 WSPC/Trim Size: 9in x 6in for Review Volume stasyuk˙new Phase Transitions in the Pseudospin-Electron Model 3The pseudospin-electron Hamiltonian (in form (1) with inclusion only of the g-interaction) was used by Müller with the aim of describing the anharmonic vibrations in the oxygen subsystem of the high-T c superconducting crystals of the YBaCuO type. 1 The YBa 2 Cu 3 O 7−δ crystal is a typical and most studied example of such objects. The unit cell contains, besides two superconducting planes, the chain (at the δ ≪ 1 composition) elements Cu 1 -O 1 , connected by Cu 1 -O 4 -Cu 2 bridges with Cu 2 -O 2 plains through the apical oxygen ions O 4 . The vibrations of these ions along the c-axis (perpendicularly to the plains) exhibit a strong anharmonicity. Much evidence exists in support of this concept. One can mention the EXAFS data, 2,3 Raman scattering and dielectric measurements, 4,5,6,7,8,9 local polaron phenomena, 10,11 bistabilities in the normal phase region 12 as well as neutron scattering investigations 13 or the results of the first principle LAPW calculations. 14 Despite a certain ambiguity in the data, the conclusions were made about the existence of two different equilibrium positions of the O 4 ion. The local double-well picture as an approximate simplified model was supported by the oxygen O 4 vacancy effect on the positions of apical ions observed in Ref. [15].Moreover, a connection between positions of O 4 ions and electron states in Cu 2 -O 2 plains plays an important role in YBa 2 Cu 3 O 7−δ crystals. The data given in Ref. [16] point to the existence of a significant correlation between the occupancy of electron states of the Cu 2 ion and the R O4−Cu2 distance as well as to the decrease of this distance at the transition from the metallic orthorombic phase to the semiconducting one (that takes place at δ > δ * = 0.55). These and other similar facts suggest the presence of a large electron-vibrational coupling. In the pseudospin representation, when the pseudospin variable S z i = ±1/2 defines the positions of O 4 ions, it is described by the gS z i n iσ term. Consideration based on the PEM was applied to the HTSC systems starting from Refs. [1,[17][18][19][20]. Hamiltonian similar to (1) was used by Hirsch and Tang in the study of electron states in the framework of cluster calculations. In the context of the idea concerning the effect of anharmonicity on the superconducting transition temperature, 17,18,19,21 the possible connection between superconducting pairing and the lattice anharmonicity was considered by Frick et al. 22 (the quantum Monte-Carlo calculations). In what follows, the investigations of the PEM were devoted to the analysis of the electron spectrum, 23 the pseudospin and collective dynamics, 24,25 the charge and pseudospin pair correlations and the behaviour of dielectric susceptibility. 26

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Section: (The Quantum Monte-carlo Calculations)mentioning

confidence: 99%

“…a) The µ = const regime. The equilibrium is defined by the minimum condition of Φ (42). Numerical analysis of solutions of equations ( 39)-( 41) which satisfy this criterion, was performed in Ref.…”

Section: The Chess-board Phasementioning

confidence: 99%

Phase Transitions in the Pseudospin-Electron Model

Stasyuk

2007

Order, Disorder and Criticality

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Raman Light Scattering in Pseudospin-Electron Model at Strong Pseudospin-Electron Interaction

Cited by 1 publication

References 18 publications

Phase Transitions in the Pseudospin-Electron Model

Phase Transitions in the Pseudospin-Electron Model

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