Temat: 75.25.Dk - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Quantum Phase Transitions in the Kitaev-Heisenberg Model on a Single Hexagon
Autorzy:: Gotfryd, D.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1385471.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
75.25.Dk
75.30.Et
Opis:: We present a detailed analysis of the Kitaev-Heisenberg model on a single hexagon. The energy spectra and spin-spin correlations obtained using exact diagonalisation indicate quantum phase transitions between antiferromagnetic and anisotropic spin correlations when the Kitaev interactions increase. In cluster mean-field approach frustrated nearest neighbor exchange stabilizes the stripe phase in between the Néel phase and frustrated one which evolves towards the Kitaev spin liquid.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 318-320
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Multiband d-p Model for the Description of Sr₂RuO₄
Autorzy:: Rościszewski, K.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1385178.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.25.Dk
75.47.Lx
71.70.Ej
Opis:: 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.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 260-262
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: On the Neglect of Local Coulomb Interaction on Oxygens in Perovskites Described by the Multiband d-p Model
Autorzy:: Rościszewski, K.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1029759.pdf
Data publikacji:: 2018-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.15.-m
75.25.Dk
75.47.Lx
Opis:: 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).
Źródło:: Acta Physica Polonica A; 2018, 133, 3; 356-358
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Stripe Phases in Layered Nickelates
Autorzy:: Rościszewski, K.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1426855.pdf
Data publikacji:: 2012-05
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.25.Dk
75.47.Lx
75.10.Lp
63.20.Pw
Opis:: 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.
Źródło:: Acta Physica Polonica A; 2012, 121, 5-6; 1048-1050
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: The Green Function Variational Approximation: Significance of Physical Constraints
Autorzy:: Bieniasz, K.
Berciu, M.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1398655.pdf
Data publikacji:: 2016-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.25.Dk
03.65.Ud
75.10.Lp
79.60.-i
Opis:: We present a calculation of the spectral properties of a single charge doped at a Cu(3d) site of the Cu-F plane in KCuF₃. The problem is treated by generating the equations of motion for the Green function by means of subsequent Dyson expansions and solving the resulting set of equations. This method, dubbed the variational approximation, is both very dependable and flexible, since it is a systematic expansion with precise control over elementary physical processes. It allows for deep insight into the underlying physics of polaron formation as well as for inclusion of many physical constraints, such as excluding crossing diagrams and double occupation constraint, which are not included in the self-consistent Born approximation. Here we examine the role and importance of such constraints by analyzing various spectral functions obtained in second order variational approximation.
Źródło:: Acta Physica Polonica A; 2016, 130, 2; 659-663
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Exotic Spin Order due to Orbital Fluctuations
Autorzy:: Brzezicki, W.
Dziarmaga, J.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1374350.pdf
Data publikacji:: 2014-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
03.65.Ud
64.70.Tg
75.25.Dk
Opis:: We investigate the phase diagrams of the spin-orbital $d^9$ Kugel-Khomskii model for increasing system dimensionality: from the square lattice monolayer, via the bilayer to the cubic lattice. In each case we find strong competition between different types of spin and orbital order, with entangled spin-orbital phases at the crossover from antiferromagnetic to ferromagnetic correlations in the intermediate regime of Hund's exchange. These phases have various types of exotic spin order and are stabilized by effective interactions of longer range which follow from enhanced spin-orbital fluctuations. We find that orbital order is in general more robust while spin order melts first under increasing temperature, as observed in several experiments for spin-orbital systems.
Źródło:: Acta Physica Polonica A; 2014, 126, 4a; A-40-A-49
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Order in Quantum Compass and Orbital e_{g} Models
Autorzy:: Czarnik, P.
Dziarmaga, J.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1029762.pdf
Data publikacji:: 2018-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
05.10.Cc
05.70.Fh
75.25.Dk
Opis:: We investigate thermodynamic phase transitions in the compass model and in e_{g} orbital model on an infinite square lattice by variational tensor network renormalization (VTNR) in imaginary time. The onset of nematic order in the quantum compass model is estimated at _{c}/J=0.0606(4). For the e_{g} orbital model one finds: (i) a very accurate estimate of _{c}/J=0.3566± 0.0001 and (ii) the critical exponents in the Ising universality class. Remarkably large difference in frustration results in so distinct values of _{c}, while entanglement influences the quality of _{c} estimation.
Źródło:: Acta Physica Polonica A; 2018, 133, 3; 359-361
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Entangled Spin-Orbital Phases in the $d^{9}$ Model
Autorzy:: Brzezicki, W.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1426843.pdf
Data publikacji:: 2012-05
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
03.65.Ud
64.70.Tg
75.25.Dk
Opis:: We investigate the phase diagrams of the spin-orbital $d^9$ Kugel-Khomskii model for a bilayer and a monolayer square lattice using the Bethe-Peierls-Weiss method. For a bilayer we obtain valence bond phases with interlayer singlets, with alternating planar singlets, and two entangled spin-orbital phases, in addition to the antiferromagnetic and ferromagnetic order. Possibility of such entangled phases in a monolayer is under investigation at present.
Źródło:: Acta Physica Polonica A; 2012, 121, 5-6; 1045-1047
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: Hole Propagation in the Orbital Compass Models
Autorzy:: Brzezicki, W.
Daghofer, M.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1385190.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
03.65.Ud
64.70.Tg
75.25.Dk
Opis:: We explore the propagation of a single hole in the generalized quantum compass model which interpolates between fully isotropic antiferromagnetic phase in the Ising model and nematic order of decoupled antiferromagnetic chains for frustrated compass interactions. We observe coherent hole motion due to either interorbital hopping or due to the three-site effective hopping, while quantum spin fluctuations in the ordered background do not play any role.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 263-265
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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