Krzysztof Rościszewski

Jahn–Teller mechanism of stripe formation in doped layered La2 − xSrxNiO4 nickelates

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 Hunds 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.

Interplay between the orbital and magnetic order in monolayer La1−xSr1+xMnO4 manganites

A two-dimensional model which describes e(g) electrons in a monolayer of an undoped and half doped manganite La(1-x)Sr(1+x)MnO(4) is studied using correlated wavefunctions. The effective Hamiltonian takes into account the kinetic energy, the crystal field splitting between x(2)-y(2) and 3z(2)-r(2) orbitals, and on-site Coulomb interactions for e(g) electrons. They interact with S = 3/2 spins due to t(2g) electrons, which are treated as frozen core spins. Furthermore, the model includes antiferromagnetic superexchange interaction between core spins, and the coupling between e(g) electrons and Jahn-Teller modes. The model reproduces the antiferromagnetic order in the undoped LaSrMnO(4) compound, with occupied 3z(2)-r(2) orbitals and elongated MnO(6) octahedra along the direction perpendicular to the Mn-O plane. In half doped La(0.5)Sr(1.5)MnO(4) manganite one finds robust chequerboard-like charge order using realistic parameters. However, the experimentally observed CE phase is more difficult to stabilize, and we discuss the necessary conditions to obtain it within the present model. Altogether, we conclude that the Jahn-Teller effect plays a crucial role in the entire regime of doping.

Charge-transfer model for the electronic structure of layered ruthenates

Motivated by the earlier experimental results and \textit{ab initio} studies on the electronic structure of layered ruthenates (Sr

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

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A possibility of high spin hole states in doped CoO2 layered systems

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Jahn–Teller distortions and the magnetic order in the perovskite manganites

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Electron correlations—the origin of the CE phase in bilayer La2−2xSr1+2xMn2O7 manganites

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Multiband model for the electronic structure of Sr2TiO4

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d−p model and spin-orbital order in vanadium perovskites

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On the Neglect of Local Coulomb Interaction on Oxygens in Perovskites Described by the Multiband d-p Model

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