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Accueil du site > Séminaires > Séminaires 2010 > Spin-orbit entanglement in Mott insulators : new route to exotic phases

mercredi 15 septembre — 14:00, attention, horaire exceptionnel

Spin-orbit entanglement in Mott insulators : new route to exotic phases

George Jackeli, Max Planck Institute for Solid State Research (Stuttgart)

par Pierre Pujol - 15 septembre 2010

n the last few years, there has been an upsurge of interest in transition metal compounds in which unusual phases may emerge due to a relativistic spin-orbit interaction. I will report our recent results on the effects of spin-orbit coupling in Mott insulators.

First, we discuss the ground state phases of a spin one-half Hamiltonian on a honeycomb lattice describing the exchange interactions between Kramers doublets of Ir$^4+$ ions in a family of layered iridates $A_2$IrO$_3$ ($A$=Li, Na). The Hamiltonian interpolates between Heisenberg and an exactly solvable Kitaev models, depending on microscopic parameters [1,2]. The model exhibits rich phase behavior [2], with an extended spin-liquid phase near the Kitaev limit, and a conventional N\’eel state close to the Heisenberg limit. The two phases are separated by a stripy antiferromagnetic order.

We next show that the spin-orbit interaction in a system of $d^1$-ions on a square lattice may drive a magnetically hidden order in which the expectation values of the local spin and orbital moments both vanish. The order parameter responsible for a time-reversal symmetry breaking has a composite nature and is a spin-orbital analog of a magnetic octupole. We argue that such a hidden order is realized in the layered perovskite Sr$_2$VO$_4$ [3].

[1] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 102, 017205 (2009).

[2] J. Chaloupka, G. Jackeli and G. Khaliullin, arXiv:1004.2964.

[3] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 103, 067205 (2009).