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Exotic Spin Order due to Orbital Fluctuations

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Brzezicki W., Dziarmaga J., Oleś A.

Acta Physica Polonica A

2014

vol. 126

issue 4a

A-40-A-49

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.

Order in Quantum Compass and Orbital e_{g} Models

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Czarnik P., Dziarmaga J., Oleś A.

Acta Physica Polonica A

2018

vol. 133

issue 3

359-361

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 𝓣_{c}/J=0.0606(4). For the e_{g} orbital model one finds: (i) a very accurate estimate of 𝓣_{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 𝓣_{c}, while entanglement influences the quality of 𝓣_{c} estimation.

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2 Acta Physica Polonica A

1 2018

1 2014

2 Dziarmaga J.

2 Oleś A.

1 Brzezicki W.

1 Czarnik P.

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Exotic Spin Order due to Orbital Fluctuations

Order in Quantum Compass and Orbital e_{g} Models