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arXiv 0906.4462cond-mat.str-el
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量子罗盘梯的精确解

Exact solution for a quantum compass ladder

Wojciech Brzezicki, Andrzej M. Oles

摘要:

我们引入了一个自旋阶梯与反铁磁伊辛ZZ相互作用沿腿,和相互作用的梯级之间的伊辛阶梯和量子罗盘阶梯。我们表明,整个能量谱的梯子可以确定的有限数量的自旋2N通过映射到量子伊辛链和使用Jordan-Wigner变换在不变的子空间。利用有限尺寸标度,我们还证明了具有自旋缺陷的子空间导致激发态,而基态对应于没有缺陷的量子伊辛模型。在量子相变到罗盘梯的最大阻挫相互作用时,梯级上的ZZ自旋关联函数坍缩为零,基态简并度增加2。我们制定了一个系统的方法来计算的配分函数的介观系统,并利用它来证明,破碎的指南针阶梯的扭结缺陷随温度的升高而增加。由2N=104个自旋组成的大罗盘阶梯的热容揭示了两个相关的能量标度,并由于密集的能谱而具有宽的最大值。本文的精确结果阐明了二维Compass模型中从有序到无序基态的量子相变的本质。

英文摘要:

We introduce a spin ladder with antiferromagnetic Ising ZZ interactions along the legs, and interactions on the rungs which interpolate between the Ising ladder and the quantum compass ladder. We show that the entire energy spectrum of the ladder may be determined exactly for finite number of spins 2N by mapping to the quantum Ising chain and using Jordan-Wigner transformation in invariant subspaces. We also demonstrate that subspaces with spin defects lead to excited states using finite size scaling, and the ground state corresponds to the quantum Ising model without defects. At the quantum phase transition to maximally frustrated interactions of the compass ladder, the ZZ spin correlation function on the rungs collapses to zero and the ground state degeneracy increases by 2. We formulate a systematic method to calculate the partition function for a mesoscopic system, and employ it to demonstrate that fragmentation of the compass ladder by kink defects increases with increasing temperature. The obtained heat capacity of a large compass ladder consisting of 2N=104 spins reveals two relevant energy scales and has a broad maximum due to dense energy spectrum. The present exact results elucidate the nature of the quantum phase transition from ordered to disordered ground state found in the compass model in two dimensions.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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