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arXiv 1104.4707cond-mat.str-el
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自旋空位对Kitaev-Heisenberg模型磁性的影响

Effects of spin vacancies on magnetic properties of the Kitaev-Heisenberg model

Fabien Trousselet, Giniyat Khaliullin, Peter Horsch

摘要:

我们研究了磁场中Kitaev-Heisenberg模型的基态性质,并探讨了非磁空位存在时自旋关联的演化。通过精确对角化,无空位相图被确定为磁场和Kitaev和Heisenberg相互作用之间的比率的函数。我们发现,在(反铁磁)条纹有序相的静态磁化率和它的各向异性可以描述的自旋倾斜机制。这也解释了当微扰包括量子涨落时向极化相的转变。自旋空位的效应敏感地依赖于基态的类型。在液相中,确定了小场中单个空位周围的磁化模式,其空间各向异性与场和/或海森堡相互作用诱导的非零进一步邻近相关性有关。在条纹阶段,空位和小场的联合作用打破了模型的六重对称性,并稳定了特定的条纹图案。由于空位之间的有效相互作用,即使在零场下也会发生类似的破缺效应。这种选择机制和空位位置的内在随机性可能导致自旋玻璃行为。

英文摘要:

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. 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. This accounts 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 around a single vacancy in a small field is determined, and its spatial anisotropy is related to that of non-zero further neighbor correlations induced by the field and/or Heisenberg interactions. In the stripe phase, the joint effect 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 effective interactions between vacancies. This selection mechanism and intrinsic randomness of vacancy positions may lead to spin-glass behavior.

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