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arXiv 1808.05656cond-mat.dis-nn
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一维保序拓扑多体定域相的分类

Classification of symmetry-protected topological many-body localized phases in one dimension

Amos Chan, Thorsten B. Wahl

摘要:

本文给出了一维多体定域自旋和费米子系统的保序拓扑相的分类。对于自旋系统,使用张量网络,我们表明,这些阶段的所有本征态具有相同的拓扑指数定义为SPT基态。对于酉在位对称性,MBL相位因此由对称群的第二上同调群的元素标记。对于反酉在位对称性也得到了类似的分类,时间反演对称性是具有$\mathbb{Z}_2$分类的特殊情况(参见。[Phys.Rev.B98,054204(2018)])。对于费米子MBL相的分类,我们提出了一个费米子张量网络图解公式。我们发现,费米MBL系统的(反)酉对称性的分类的(广义)第二上同调群的元素,如果宇称是包括在对称群。然而,我们的方法错过了一个$\mathbb{Z}_2$拓扑指数预期从分类的费米子SPT基态。此外,我们发现所有阶段是稳定的任意保序局部扰动。相反,不同的拓扑相位必须由离域本征态标记的跃迁分开。最后,我们证明了自旋系统的分类是完整的,在这个意义上,不能有任何额外的拓扑指数有关的个人本征态的属性,但可以有额外的拓扑指数,进一步分类哈密顿。

英文摘要:

We provide a classification of symmetry-protected topological (SPT) phases of many-body localized (MBL) spin and fermionic systems in one dimension. For spin systems, using tensor networks we show that all eigenstates of these phases have the same topological index as defined for SPT ground states. For unitary on-site symmetries, the MBL phases are thus labeled by the elements of the second cohomology group of the symmetry group. A similar classification is obtained for anti-unitary on-site symmetries, time-reversal symmetry being a special case with a $\mathbb{Z}_2$ classification (cf. [Phys. Rev. B 98, 054204 (2018)]). For the classification of fermionic MBL phases, we propose a fermionic tensor network diagrammatic formulation. We find that fermionic MBL systems with an (anti-)unitary symmetry are classified by the elements of the (generalized) second cohomology group if parity is included into the symmetry group. However, our approach misses a $\mathbb{Z}_2$ topological index expected from the classification of fermionic SPT ground states. Furthermore, we show that all found phases are stable to arbitrary symmetry-preserving local perturbations. Conversely, different topological phases must be separated by a transition marked by delocalized eigenstates. Finally, we demonstrate that the classification of spin systems is complete in the sense that there cannot be any additional topological indices pertaining to the properties of individual eigenstates, but there can be additional topological indices that further classify Hamiltonians.

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