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The Novel Spin-Charge Patterns in Correlated Electron Systems Described by Extended Hubbard Hamiltonian

100%
Rościszewski K., Oleś A.
Acta Physica Polonica A
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2004
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vol. 105
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issue 5
495-500
EN
Inhomogeneous spin and charge orderings in doped two-dimensional correlated electron systems described by the extended Hubbard Hamiltonian were investigated. At the crossover from stripe phases to charge order phases, the novel types of ordering connected with highly symmetric superlattice-type spin and charge patterns were identified. In particular, the emergence of local hexagonal-like symmetry is of interest as such patterns are generic in complex, nonlinear dynamic systems.
2
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Interrelation between the Optical Conductivity and Crystal Field Splitting in Monolayer Manganites

100%
Rościszewski K., Oleś A.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
107-109
EN
We introduce an effective model for correlated e_g electrons which reproduces qualitatively the evolution of magnetic order in monolayer manganites when correlated wave functions are used. Here we address recent optical conductivity measurements suggesting that the splitting between the occupied and empty e_g states is very large in LaSrMnO_4, contrary to what is expected for the effective model. We argue that no contradiction was found but several simple-minded one-atom-based expectations concerning crystal-field splitting and optical conductivity are in error.
3
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On the Neglect of Local Coulomb Interaction on Oxygens in Perovskites Described by the Multiband d-p Model

100%
Rościszewski K., Oleś A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
356-358
EN
On the example of TiO₄ layer (such as realized in Sr₂TiO₄) we study electronic structure of multiband d-p models describing transition metal perovskites. As suggested by experiment, the studied system is predicted to be a robust nonmagnetic insulator. A realistic treatment of electronic structure requires one to introduce non-zero Coulomb local interactions at 2p oxygen orbitals. However, up till now majority of papers based upon multiband models made an approximation of neglecting such interactions. We show that this simplification does not lead to serious problems in predictions of the electronic structure provided the Coulomb interactions at titanium ions and charge transfer gap are suitably renormalized (so they become entirely different with respect to the true microscopic d-p model parameters).
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Multiband d-p Model for the Description of Sr₂RuO₄

100%
Rościszewski K., Oleś A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
260-262
EN
We study electronic structure of multiband d-p model describing RuO₄ layer such as realized in Sr₂RuO₄. The model takes into account nearest-neighbor anisotropic ruthenium-oxygen and oxygen-oxygen hoppings, intra-atomic Coulomb interaction, Hund's exchange and in addition spin-orbit coupling on ruthenium. The RuO₄ is universally considered as a pure t_{2g} system (with e_{g} orbitals empty) due to sizable gap between t_{2g} and e_{g} levels. We show that ruthenium e_{g} orbitals are in fact occupied, similarly like showed earlier for CoO₂ layers.
5
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Stripe Phases in Layered Nickelates

100%
Rościszewski K., Oleś A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1048-1050
EN
To describe quasi two-dimensional nickelates we introduce an effective Hamiltonian for e_{g} electrons, which includes the kinetic energy, on-site Coulomb interactions, spin-spin and Jahn-Teller (static) terms. The experimental stripe phases are correctly reproduced by the model. The mechanisms responsible for stripe formation are different than those reported in cuprates and manganites.
6
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Stripe Phases in the Hubbard Model

81%
Góra D., Rościszewski K., Oleś A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
225-228
EN
We investigate the magnetic and charge ordering in the stripe phases obtained while using correlated wave functions for finite 8×8 clusters described by the Hubbard model with extended hopping. Nonmagnetic vertical (01) site-centered domain walls and (11) bond-centered stripes are found for the parameters of La_{2-x}Sr_{x}CuO_{4} and YBa_{2}Cu_{3}O_{6+x}, respectively, at doping δ=1/8. The obtained half-filled domain nonmagnetic walls reproduce the maxima observed in neutron scattering for La_{2-x}Sr_{x}CuO_{4}.
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