Autor: Oleś, Andrzej - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Charge and Orbital Order in Transition Metal Oxides
Autorzy:: Oleś, Andrzej
Powiązania:: https://bibliotekanauki.pl/articles/1536553.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
75.30.Et
03.67.Mn
61.50.Ks
Opis:: 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.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 212-231
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Frustration and Entanglement in Compass and Spin-Orbital Models
Autorzy:: Oleś, Andrzej
Powiązania:: https://bibliotekanauki.pl/articles/1384027.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
64.70.Tg
75.25.Dk
79.60.-i
Opis:: We review the consequences of intrinsic frustration of the orbital superexchange and of spin-orbital entanglement. While the Heisenberg perturbing interactions remove frustration in the compass model, the lowest columnar excitations are robust in the nanoscopic compass clusters and might be used for quantum computations. Entangled spin-orbital states determine the ground states in some cases, while in others concern excited states and lead to measurable consequences, as in the RVO₃ perovskites. On-site entanglement for strong spin-orbit coupling generates the frustrated Kitaev-Heisenberg model with a rich magnetic phase diagram on the honeycomb lattice. Frustration is here reflected in hole propagation which changes from coherent in an antiferromagnet via hidden quasiparticles in zigzag and stripe phases to entirely incoherent one in the Kitaev spin liquid.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 163-169
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Spin-Orbital Physics in Transition Metal Oxides
Autorzy:: Oleś, Andrzej
Powiązania:: https://bibliotekanauki.pl/articles/1810283.pdf
Data publikacji:: 2009-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
75.30.Et
03.67.Mn
61.50.Ks
Opis:: We present the main features of the spin-orbital superexchange which describes the magnetic and optical properties of the Mott insulators with orbital degrees of freedom. In contrast to the SU(2) symmetry of spin superexchange, the orbital part of the superexchange obeys the lower cubic symmetry of the lattice and is intrinsically frustrated. This intrinsic frustration and spin-orbital entanglement induce enhanced quantum fluctuations, and we point out a few situations where this leads to disordered states. Strong coupling between the spin and orbital degrees of freedom is discussed on the example of the $RVO_3$ perovskites, with R standing for rare-earth ion, La,...,Lu. We explain the observed evolution of the orbital $T_{OO}$ and Néel $T_{N1}$ transition temperature in the $RVO_3$ series with decreasing ionic radius $r_R$. A few open problems and the current directions of research in the field of spin-orbital physics are pointed out.
Źródło:: Acta Physica Polonica A; 2009, 115, 1; 36-46
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Stripes and Pairing in High Temperature Superconductors
Autorzy:: Oleś, Andrzej M.
Powiązania:: https://bibliotekanauki.pl/articles/1431206.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.10.Jm
75.30.Et
03.67.Mn
61.50.Ks
Opis:: We review briefly several approaches used to investigate the stability of stripe phases in high temperature superconductors, where charge inhomogeneities arise from competing kinetic and magnetic energies. The mechanism of stripe formation, their consequences for the normal state and enhancement of pairing interaction triggered by charge inhomogeneities are briefly summarized. Finally, we demonstrate that orbital degeneracy (i) leads to a more subtle mechanism of stripe formation, and (ii) plays an important role and determines the symmetry of the superconducting state in pnictides.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 752-758
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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