|
Fabien Trousselet, Giniyat Khaliullin, and Peter Horsch
We study a model of localized spins on the honeycomb lattice interacting via nearest-neighbour Heisenberg interactions along with those of the Kitaev model. This model can be realized in orbitally degenerate materials with a strong spin-orbit coupling, selecting at each transition metal atom a doublet of states defining a pseudospin 1/2; various exchange processes between neighbouring pseudospins result in the Kitaev-Heisenberg model. It has been previously shown that the spin liquid phase characteristic of the Kitaev model persists up to a finite amplitude of Heisenberg interactions, after which a stripe order develops [1]. Candidate material(s) - for instance Na2IrO3 - are subject to non negligible site-mixing between Na and Ir atoms [2]. This rises the question of whether non-magnetic defects can shift the transition between liquid and ordered phases. We adress this question by means of exact diagonalization on periodic clusters, supplemented by perturbative reasonments. We find that neighbouring defects pairs select, depending on their respective positions, a given orientation for stripes in the ordered phase, and may slightly stabilize this phase w.r.t. the liquid. The possibility of a glassy phase that could exist in large systems, due to the competition between different stripe orientations in neighbouring nanodomains, remains an interesting issue. Besides, we also consider the influence of a uniform magnetic field, as a tool to study the structure of low-energy states without and with defects. [1] J. Chaloupka, G. Jackeli, G. Khaliullin, PRL 105, 027204 (2010). [2] Y. Singh, P. Gegenwart, PRB 82, 064412 (2010). |
|