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Entangled Spin-Orbital Phases in the d^{9} Model

100%
Brzezicki W., Oleś A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1045-1047
EN
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.
2
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Quantum Phase Transition in the One-Dimensional XZ Model

100%
Brzezicki W., Oleś A.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
162-164
EN
We introduce a one-dimensional XZ model with alternating σ_i^zσ_{i+1}^z and σ_i^xσ_{i+1}^x interactions on even/odd bonds, interpolating between the Ising model and the quantum compass model. We present two ways of its exact solution by: (i) mapping to the quantum Ising models, and (ii) using fermions with spin 1/2. In certain cases the nearest neighbor pseudospin correlations change discontinuously at the quantum phase transition, where one finds highly degenerate ground state of the 1D compass model.
3
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Hole Propagation in the Orbital Compass Models

81%
Brzezicki W., Daghofer M., Oleś A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
263-265
EN
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.
4
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Exotic Spin Order due to Orbital Fluctuations

81%
Brzezicki W., Dziarmaga J., Oleś A.
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vol. 126
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issue 4a
A-40-A-49
EN
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.
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