Pseudospin–electron model of intercalation

Mysakovych, T. S.; Stasyuk, I. V.

doi:10.30970/jps.11.195

Cited by 3 publications

(6 citation statements)

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“…Numerical calculations performed in Ref. [34] show that the SC transition in the simplified PEM is possible (in the weak coupling case) at the electron concentrations away from half-filling (when the chemical potential is placed near the electron band edges) and outside the region of the above described transitions with the modulation of the electron and pseudospin density (see Fig. 26).…”

Section: Superconductivity In the Pemmentioning

confidence: 97%

“…29,30 The possibility of the appearance of a doubly modulated (so-called chessboard) phase or an incommensurate phase (in the case of weak coupling) was established; 31,32,33 the superconducting instability in PEM was analysed. 34 In the case of two-sublattice PEM the structural instabilities of the ferroelectric type as well as the bistability phenomena were revealed and analysed. 35,36,37,38 The study of the PEM thermodynamics was performed mainly within the generalized random phase approximation (GRPA).…”

Section: (The Quantum Monte-carlo Calculations)mentioning

confidence: 99%

“…It was just the point of investigation performed in Ref. [34] within the GRPA. To examine the possibility of the appearance of SC phase we calculated the static susceptibility χ SC in the superconducting channel.…”

Section: Superconductivity In the Pemmentioning

confidence: 99%

“…69,70 In calculations performed in Ref. [34], the approximation Γ 0 ≈ −g 2 Σ, similar to the non-renormalized ME approximation in the Holstein model, 69 was used. This can be done in the high-temperature phase, when the system has not still passed to the CDW state.…”

Section: Superconductivity In the Pemmentioning

confidence: 99%

“…The estimates performed in Ref. [34] show that at W ≈ 0.5 eV and g ≈ 0.25 eV, the maximum value of the SC transition temperature is T SC max ≈ 10 − 40 K. This agrees with the conclusions obtained for PEM in Ref. [67], where calculations were performed by analogy with the scheme used for the Eliashberg equations in the limit of a weak electron-phonon interaction, provided that the renormalization of the pseudospin excitation energy is neglected.…”

Section: Superconductivity In the Pemmentioning

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: Superconductivity In the Pemmentioning

confidence: 97%

Section: (The Quantum Monte-carlo Calculations)mentioning

confidence: 99%

Section: Superconductivity In the Pemmentioning

confidence: 99%

Section: Superconductivity In the Pemmentioning

confidence: 99%

Section: Superconductivity In the Pemmentioning

confidence: 99%

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Phase Transitions in the Pseudospin-Electron Model

Stasyuk

2007

Order, Disorder and Criticality

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Bose–Fermi–Hubbard model: Pseudospin operator approach

Mysakovych

2011

Physica B: Condensed Matter

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Phase diagrams of the Bose–Fermi–Hubbard model at finite temperature

Mysakovych

2010

J. Phys.: Condens. Matter

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The phase transitions at finite temperatures in the systems described by the Bose-Fermi-Hubbard model are investigated in this work in the framework of the self-consistent random phase approximation. The case of the hard-core bosons is considered and the pseudospin formalism is used. The density-density correlator is calculated in the random phase approximation and the possibilities of transitions from superfluid to supersolid phases are investigated. It is shown that the transitions between uniform and charge-ordered phases can be of the second or the first order, depending on the system parameters.

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Pseudospin–electron model of intercalation

Cited by 3 publications

References 0 publications

Phase Transitions in the Pseudospin-Electron Model

Phase Transitions in the Pseudospin-Electron Model

Bose–Fermi–Hubbard model: Pseudospin operator approach

Phase diagrams of the Bose–Fermi–Hubbard model at finite temperature

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