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arXiv 1709.03508cond-mat.mes-hallcond-mat.str-el
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量子临界链中的拓扑和边模

Topology and edge modes in quantum critical chains

Ruben Verresen, Nick G. Jones, Frank Pollmann

摘要:

我们表明,拓扑结构可以保护指数本地化,零能量边缘模式之间的一维对称保护拓扑相位的临界点。即使主体中没有间隙自由度,这也是可能的--与最近关于无间隙链中边缘模式的工作相反。我们提出了一个直观的图片的情况下,这些边缘模式的存在与时间反演对称性(BDI类的十倍的方式)的非相互作用的无自旋费米子。这种现象的稳定性依赖于一个拓扑不变量定义在一个复杂的功能,计算其零点和极点内的单位圆。这个不变量可以防止由\emph{same}共形场论(CFT)描述的两个模型光滑连接。在非相互作用的BDI类的临界阶段的一个完整的分类:每个阶段被标记的CFT,$c \in \frac{1}{2}\mathbb N$,和拓扑不变量,$ω\in \mathbb Z$的中心荷。此外,$c$由与转变相邻的相位之间的边缘模式的数量差确定。数值模拟表明,临界链的拓扑边模在相互作用和无序存在的情况下是稳定的。

英文摘要:

We show that topology can protect exponentially localized, zero energy edge modes at critical points between one-dimensional symmetry protected topological phases. This is possible even without gapped degrees of freedom in the bulk ---in contrast to recent work on edge modes in gapless chains. We present an intuitive picture for the existence of these edge modes in the case of non-interacting spinless fermions with time reversal symmetry (BDI class of the tenfold way). The stability of this phenomenon relies on a topological invariant defined in terms of a complex function, counting its zeros and poles inside the unit circle. This invariant can prevent two models described by the \emph{same} conformal field theory (CFT) from being smoothly connected. A full classification of critical phases in the non-interacting BDI class is obtained: each phase is labeled by the central charge of the CFT, $c \in \frac{1}{2}\mathbb N$, and the topological invariant, $ω\in \mathbb Z$. Moreover, $c$ is determined by the difference in the number of edge modes between the phases neighboring the transition. Numerical simulations show that the topological edge modes of critical chains can be stable in the presence of interactions and disorder.

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