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arXiv 0907.1693cond-mat.str-el
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阻挫反铁磁体中的自旋-晶格耦合

Spin-lattice coupling in frustrated antiferromagnets

O. Tchernyshyov, G. -W. Chern

摘要:

本文综述了自旋-晶格耦合在消除烧绿石反铁磁体,特别是尖晶石氧化物的几何阻挫中的作用机制。烧绿石晶格的组成单元四面体单元在晶格自由度与反铁磁性耦合时发生自旋驱动的Jahn-Teller不稳定性。通过限制我们的考虑,以保持平移对称性的晶格的扭曲,我们提出了一个一般的理论,集体自旋Jahn-Teller效应的烧绿石晶格。预测的晶格畸变之一打破了反转对称性,并产生了手性烧绿石晶格,其中受挫键形成具有一定手性的螺旋。手性通过自旋轨道耦合转移到自旋系统,导致长周期螺旋状态,如在尖晶石CdCr 2 O 4中观察到的。我们讨论了利用局域声子模的自旋-晶格耦合的显式模型,以及它们在其他阻挫磁体中的应用。

英文摘要:

We review the mechanism of spin-lattice coupling in relieving the geometrical frustration of pyrochlore antiferromagnets, in particular spinel oxides. The tetrahedral unit, which is the building block of the pyrochlore lattice, undergoes a spin-driven Jahn-Teller instability when lattice degrees of freedom are coupled to the antiferromagnetism. By restricting our considerations to distortions which preserve the translational symmetries of the lattice, we present a general theory of the collective spin-Jahn-Teller effect in the pyrochlore lattice. One of the predicted lattice distortions breaks the inversion symmetry and gives rise to a chiral pyrochlore lattice, in which frustrated bonds form helices with a definite handedness. The chirality is transferred to the spin system through spin-orbit coupling, resulting in a long-period spiral state, as observed in spinel CdCr2O4. We discuss explicit models of spin-lattice coupling using local phonon modes, and their applications in other frustrated magnets.

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