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arXiv 1105.3785cond-mat.str-el
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简并Shastry-Sutherland基态反铁磁体的三重子平均场分析

Triplon mean-field analysis of an antiferromagnet with degenerate Shastry-Sutherland ground states

Rakesh Kumar, Brijesh Kumar

摘要:

本文研究了具有简并Shastry-Sutherland基态的正方晶格上的自旋$\frac{1}{2}$反铁磁体的量子相图,迄今为止只知道一个示意性的相图。许多奇异的相提出了在示意相图中使用精确对角化非常小的系统尺寸。在我们目前的工作中,这一反铁磁体的一个重要的推广,并在热力学极限下使用三重子平均场论进行了研究。值得注意的是,这种反铁磁体显示出稳定的元格自旋带隙相,就像原来的Shastry-Sutherland反铁磁体一样,尽管这两种反铁磁体在哈密顿结构和基态简并度上不同。我们提出了一个亚晶格柱状二聚体相,这是稳定的第二和第三邻居反铁磁海森堡交换相互作用。还有一些公度和非公度磁有序相,以及其他自旋能隙相,它们在量子相图中找到了自己的位置。平均场的结果表明,两个自旋能隙之间总是存在一个能级交叉相变,而在其他情况下,要么发生能级交叉或连续的相变。

英文摘要:

We look into the quantum phase diagram of a spin-$\frac{1}{2}$ antiferromagnet on the square lattice with degenerate Shastry-Sutherland ground states, for which only a schematic phase diagram is known so far. Many exotic phases were proposed in the schematic phase diagram by the use of exact diagonalization on very small system sizes. In our present work, an important extension of this antiferromagnet is introduced and investigated in the thermodynamic limit using triplon mean-field theory. Remarkably, this antiferromagnet shows a stable plaquette spin-gapped phase like the original Shastry-Sutherland antiferromagnet, although both of these antiferromagnets differ in the Hamiltonian construction and ground state degeneracy. We propose a sublattice columnar dimer phase which is stabilized by the second and third neighbor antiferromagnetic Heisenberg exchange interactions. There are also some commensurate and incommensurate magnetically ordered phases, and other spin-gapped phases which find their places in the quantum phase diagram. Mean-field results suggest that there is always a level-crossing phase transition between two spin gapped phases, whereas in other situations, either a level-crossing or a continuous phase transition happens.

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