How strongly are electrons correlated in the high-Tc superconducting materials?

Oleś, Andrzej M.; Zaanen, Jan; Fulde, Peter

doi:10.1016/0378-4363(87)90205-1

Cited by 45 publications

(26 citation statements)

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“…This delocalization implies that also Ba ions cannot be considered as Ba 2+ which would be the case of the idealistic ionic model. Furthermore, using the analogy to cuprates, we suggest that also CuO 2 planes in the undoped high-T c materials [40,[51][52][53] cannot be considered as charged formally in the same way as predicted in the ionic model, i.e., Cu 2+ O…”

Section: Discussion and Summarymentioning

confidence: 99%

Multibandd−pmodel and self-doping in the electronic structure ofBa2IrO4

Rościszewski

Oleś

2016

Phys. Rev. B

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We introduce and investigate the multiband d − p model describing a IrO4 layer (such as realized in Ba2IrO4) where all 34 orbitals per unit cell are partly occupied, i.e., t2g and eg orbitals at iridium and 2p orbitals at oxygen ions. The model takes into account anisotropic iridium-oxygen d − p and oxygen-oxygen p − p hopping processes, crystal-field splittings, spin-orbit coupling, and the on-site Coulomb interactions, both at iridium and at oxygen ions. We show that the predictions based on assumed idealized ionic configuration (with n0 = 5 + 4 × 6 = 29 electrons per IrO4 unit) do not explain well the independent ab initio data and the experimental data for Ba2IrO4. Instead we find that the total electron density in the d − p states is smaller, n = 29 − x < n0 (x > 0). When we fix x = 1, the predictions for the d − p model become more realistic and weakly insulating antiferromagnetic ground state with the moments lying within IrO2 planes along (110) direction is found, in agreement with experiment and ab initio data. We also show that: (i) holes delocalize over the oxygen orbitals and the electron density at iridium ions is enhanced, hence (ii) their eg orbitals are occupied by more than one electron and have to be included in the multiband d − p model describing iridates.

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Section: Discussion and Summarymentioning

confidence: 99%

Multibandd−pmodel and self-doping in the electronic structure ofBa2IrO4

Rościszewski

Oleś

2016

Phys. Rev. B

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“…The parameters for the cuprates which follow from the electronic structure calculations are (all in eV) [22]: ∆ = 3.6, t pd = 1.3, t pp = 0.65, U d ≈ 10.5, U d ≈ 4.0. Electron correlations are moderate in spite of the large value of U d [19], but they suffice to localize holes at Cu sites in the undoped system, such as La 2 CuO 4 or YBa 2 Cu 3 O 6 . Taking the above parameters, ∆ U d and these systems are charge transfer insulators, in contrast to the perovskite titanates and vanadates, which are the Mott-Hubbard systems [1].…”

Section: Degrees Of Freedom In Transition Metal Oxidesmentioning

confidence: 99%

“…where γ H stands for the contribution due to the high-spin states proportional to the Hund exchange (19) and stabilizes FM spin order. While the spin and orbital operators are disentangled in the FM ground state, one may consider a coupled FM spin chain to an orbital chain with interactions which favor the AO order, as realized in the C-AF phase.…”

Section: Peierls Dimerization In Yvomentioning

confidence: 99%

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Charge and Orbital Order in Transition Metal Oxides

Oleś

2010

Acta Phys. Pol. A

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A short introduction to the complex phenomena encountered in transition metal oxides with either charge or orbital or joint charge-and-orbital order, usually accompanied by magnetic order, is presented. It is argued that all the types of above ordered phases in these oxides follow from strong Coulomb interactions as a result of certain compromise between competing instabilities towards various types of magnetic order and optimize the gain of kinetic energy in doped systems. This competition provides a natural explanation of the stripe order observed in doped cuprates, nickelates and manganites. In the undoped correlated insulators with orbital degrees of freedom the orbital order stabilizes particular types of anisotropic magnetic phases, and we contrast the case of decoupled (disentangled) spin and orbital degrees of freedom in the manganites with entangled spin-orbital states which decide about certain rather exotic phenomena observed in the perovskite vanadates at finite temperature. Examples of successful concepts in the theoretical approaches to these complex systems are given and some open problems of current interest are indicated. Degrees of freedom in transition metal oxidesThe physical properties of transition metal oxides are driven by strong electron interactions [1]. It is due to strong local Coulomb interactions that these systems exhibit very interesting and quite diverse instabilities towards ordered magnetic phases when doping x or temperature T is varied -is some cases also with orbital order. These instabilities are observed, inter alia, in rapid changes of the transport properties at the metalinsulator phase transitions, or in the onset of superconductivity.One of the outstanding problems in modern condensed matter theory is the description of strongly correlated electrons in various systems. When local Coulomb interactions are strong, the usual methods used for calculating the electronic structure fail and have to be extended by the terms following from local interactions, either in the framework of the local density approximation (LDA) with Coulomb U , the so-called LDA+U method [2], or by the self-energy within the dynamical mean-field theory (DMFT) [3], in the LDA + DMFT approach [4]. This latter approach makes use of the local self-energy which becomes exact in the limit of infinite spatial dimension d = ∞ [5]. However, even these methods cannot overcome certain shortcomings of the effective one-particle theory which justifies modelling of the transition metal * Dedicated to the memory of the late Professor Jan Stankowski. * * e-mail: a.m.oles@fkf.mpg.de oxides with Hamiltonians of the Hubbard type, and looking for solutions with methods of quantum many-body theory. The advantage of recent rapid progress in the electronic structure calculations is that such models can use realistic parameters nowadays, which follow from the electronic structure calculations for a given system. Although the field of strongly correlated electronic systems is very rich, we shall concentrate here on the phe...

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“…This ansatz was successfully applied to several systems, inter alia to cuprates [42], nickelates [43], manganites [19] and chemical bonds in molecular systems [44]. Here the HF computations were run starting from each one of many different initial conditions (to get unbiased results we considered up to 10000 nonhomogeneous random charge and spin arrangements for each doping level).…”

Section: Computational Detailsmentioning

confidence: 99%

A possibility of high spin hole states in doped CoO₂layered systems

Rościszewski¹,

Oleś²

2013

J. Phys.: Condens. Matter

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Abstract. We introduce and investigate an effective five-band model for t 2g and e g electrons to describe doped cobalt oxides with Co 3+ and Co 4+ ions in two-dimensional CoO 2 triangular lattice layers, as in Na 1−x CoO 2 . The effective Hamiltonian includes anisotropic kinetic energy (due to both direct Co-Co and indirect Co-O-Co hoppings), on-site Coulomb interactions parameterized by intraorbital Hubbard repulsion U and full Hund's exchange tensor, crystal-field terms and Jahn-Teller static distortions. We study it using correlated wave functions on 6 × 6 clusters with periodic boundary conditions. The computations indicate low S = 0 spin to high S = 2 spin abrupt transition in the undoped systems when increasing strength of the crystal field, while intermediate S = 1 spins are not found. Surprisingly, for the investigated realistic Hamiltonian parameters describing low spin states in CoO 2 planes, doping generates high S = 5 2 spins at Co 4+ ions that are pairwise bound into singlets, seen here as pairs of up and down spins. It is found that such singlet pairs self-organize at higher doping into lines of spins with coexisting antiferromagnetic and ferromagnetic bonds, forming stripe-like structures. The ground states are insulating within the investigated range of doping because computed HOMO-LUMO gaps are never small enough.

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How strongly are electrons correlated in the high-Tc superconducting materials?

Cited by 45 publications

References 18 publications

Multibandd−pmodel and self-doping in the electronic structure ofBa2IrO4

Multibandd−pmodel and self-doping in the electronic structure ofBa2IrO4

Charge and Orbital Order in Transition Metal Oxides

A possibility of high spin hole states in doped CoO₂layered systems

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How strongly are electrons correlated in the high-Tc superconducting materials?

Cited by 45 publications

References 18 publications

Multibandd−pmodel and self-doping in the electronic structure ofBa2IrO4

Multibandd−pmodel and self-doping in the electronic structure ofBa2IrO4

Charge and Orbital Order in Transition Metal Oxides

A possibility of high spin hole states in doped CoO2layered systems

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A possibility of high spin hole states in doped CoO₂layered systems