|
We study the ground state properties of the Kitaev-Heisenberg model in a magnetic field and explore the evolution of spin correlations in the presence of non-magnetic vacancies [1]. Such a model may be relevant for layered iridates A2IrO3 (A=Na or Li) [2]. By means of exact diagonalizations, the phase diagram without vacancies is determined as a function of the magnetic field and the ratio between Kitaev and Heisenberg interactions. We show that in the (antiferromagnetic) stripe ordered phase the static susceptibility and its anisotropy can be described by a spin canting mechanism, accounting as well for the transition to the polarized phase when including quantum fluctuations perturbatively.
Effects of spin vacancies depend sensitively on the type of the ground state. In the liquid phase, the magnetization pattern and its spatial anisotropy around a single vacancy in a small field is determined. In the stripe phase, the combination of a vacancy and a small field breaks the six-fold symmetry of the model and stabilizes a particular stripe pattern. Similar symmetry-breaking effects occur even at zero field due to interaction effects between vacancies. This selection mechanism and intrinsic randomness of vacancy positions may lead to spin-glass behavior. [1] F. Trousselet, G. Khaliullin and P. Horsch, PRB 84, 054409 (2011). [2] Y. Singh et al., PRL 108, 127203 (2012). |
|