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arXiv 1209.5895cond-mat.str-el
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三角Kitaev-Heisenberg模型基态的Z_2涡旋晶格

Z_2-vortex lattice in the ground state of the triangular Kitaev-Heisenberg model

Ioannis Rousochatzakis, Ulrich K. Rössler, Jeroen van den Brink, Maria Daghofer

摘要:

三角晶格海森堡反铁磁体(HAF)具有拓扑Z_2涡旋激发,在有限温度下形成气体。在这里,我们表明,自旋-轨道相互作用,通过Kitaev项中的交换哈密顿量,冷凝成一个三角形的$Z_2$涡旋晶体在零温度下,这些涡旋。Z_2涡旋的核心表现出突变的、类似于孤子的磁化调制,并且是由三个铁磁畴的蜂窝状超结构的特殊缠绕而产生的,三个蜂窝状超结构分别对应于纯HAF的120度态的三个子晶格中的一个。这是一个新的例子的成核转变,类似于自发形成的磁畴,Abrikosov涡在类型II超导体,蓝相在胆甾相液晶,和skyrmions在手性helimagnets。由于该机制依赖于几何阻挫和自旋轨道各向异性的相互作用,这种涡旋中间相可以在具有近六边形拓扑结构的自旋轨道耦合相关系统中实现为基态性质,如三角形或强烈阻挫的蜂窝状虹彩。

英文摘要:

The triangular-lattice Heisenberg antiferromagnet (HAF) is known to carry topological Z_2 vortex excitations which form a gas at finite temperatures. Here we show that the spin-orbit interaction, introduced via a Kitaev term in the exchange Hamiltonian, condenses these vortices into a triangular $Z_2$ vortex crystal at zero temperature. The cores of the Z_2 vortices show abrupt, soliton-like magnetization modulations and arise by a special intertwining of three honeycomb superstructures of ferromagnetic domains, one for each of the three sublattices of the 120-degree state of the pure HAF. This is a new example of a nucleation transition, analogous to the spontaneous formation of magnetic domains, Abrikosov vortices in type-II syperconductors, blue phases in cholesteric liquid crystals, and skyrmions in chiral helimagnets. As the mechanism relies on the interplay of geometric frustration and spin-orbital anisotropies, such vortex mesophases can materialize as a ground-state property in spin-orbit coupled correlated systems with nearly hexagonal topology, as in triangular or strongly frustrated honeycomb iridates.

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