Interplay between the orbital and magnetic order in monolayer La1−xSr1+xMnO4manganites

Rościszewski, Krzysztof; Oleś, Andrzej M.

doi:10.1088/0953-8984/19/18/186223

Cited by 13 publications

(51 citation statements)

References 61 publications

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“…These model calculations illustrate as well the complementarity of spin and orbital order expressed by the GoodenoughKanamori rules [75]. In these systems the short-range charge order gradually develops with increasing doping in the realistic parameter regime [134]. However, more complete models including the charge transfer physics are necessary to describe the features observed in the optical spectra, as for instance in insulating LaSrMnO 4 [135].…”

Section: Coexisting Charge and Orbital Ordermentioning

confidence: 67%

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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Section: Coexisting Charge and Orbital Ordermentioning

confidence: 67%

Charge and Orbital Order in Transition Metal Oxides

Oleś

2010

Acta Phys. Pol. A

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“…In the present study we use a Hubbard-type Hamiltonian H for two e g orbital states defined on a finite cluster: [24], where the same e g orbital degrees of freedom are present. The kinetic part H kin is expressed using two e g orbitals:…”

Section: The Effective Model Hamiltonianmentioning

confidence: 99%

“…For the present convention and for negative values of crystal field parameter (E z < 0) the z orbital is being favored over the x orbital. The H int and H spin stand for an approximate form of local Coulomb and exchange interactions for electrons within degenerate e g orbitals used before for monolayer, bilayer and cubic perovskite manganites [24],…”

Section: The Effective Model Hamiltonianmentioning

confidence: 99%

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Jahn–Teller mechanism of stripe formation in doped layered La_{2 −x}Sr_xNiO₄nickelates

Rościszewski¹,

Oleś²

2011

J. Phys.: Condens. Matter

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We introduce an effective model for e(g) electrons to describe quasi-two-dimensional layered La(2-x)Sr(x)NiO(4) nickelates and study it using correlated wavefunctions on 8 × 8 and 6 × 6 clusters. The effective Hamiltonian includes the kinetic energy, on-site Coulomb interactions for e(g) electrons (intraorbital U and Hund's exchange J(H)) and the coupling between e(g) electrons and Jahn-Teller distortions (static modes). The experimental ground state phases with inhomogeneous charge, spin and orbital order at the dopings x = 1/3 and 1/2 are reproduced very well by the model. Although the Jahn-Teller distortions are weak, we show that they play a crucial role and stabilize the observed cooperative charge, magnetic and orbital order in the form of a diagonal stripe phase at x = 1/3 doping and a chequerboard phase at x = 1/2 doping.

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“…Following them the electron correlations were studied using Local Ansatz (LA) method which implements the leading on-site electron correlations [11]. Due to high density of e g electrons per site n = 2 − x the correlation energies were found to be much larger here than those reported before for cuprates [12] or manganites [6], but they do not modify the stability of the HF ground state. In the undoped La 2 NiO 4 (N = 2 × 6 2 corresponds to n = 2 electrons per site) we found a uniform charge distribution in the ground state, with equal orbital electron densities n x = n z = 1, corresponding to a high-spin S = 1 state at each Ni 2+ ion.…”

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confidence: 88%

Stripe Phases in Layered Nickelates

Rościszewski

Oleś

2012

Acta Phys. Pol. A

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Interplay between the orbital and magnetic order in monolayer La_1−xSr_1+xMnO₄manganites

Cited by 13 publications

References 61 publications

Charge and Orbital Order in Transition Metal Oxides

Charge and Orbital Order in Transition Metal Oxides

Jahn–Teller mechanism of stripe formation in doped layered La_{2 −x}Sr_xNiO₄nickelates

Stripe Phases in Layered Nickelates

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Interplay between the orbital and magnetic order in monolayer La1−xSr1+xMnO4manganites

Cited by 13 publications

References 61 publications

Charge and Orbital Order in Transition Metal Oxides

Charge and Orbital Order in Transition Metal Oxides

Jahn–Teller mechanism of stripe formation in doped layered La2 −xSrxNiO4nickelates

Stripe Phases in Layered Nickelates

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Interplay between the orbital and magnetic order in monolayer La_1−xSr_1+xMnO₄manganites

Jahn–Teller mechanism of stripe formation in doped layered La_{2 −x}Sr_xNiO₄nickelates