arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1507.01635cond-mat.dis-nncond-mat.mes-hallcond-mat.stat-mech
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多体局域化-离域相变判据

A criterion for many-body localization-delocalization phase transition

Maksym Serbyn, Z. Papić, Dmitry A. Abanin

摘要:

我们提出了一种新的方法来探测遍历性及其崩溃的量子多体系统的基础上,他们的本地微扰的响应。我们研究了系统的本征态之间的本地运营商的矩阵元素的分布,发现在多体本地化(MBL)和遍历阶段的定性不同的行为。为了描述局域扰动对本征态的影响程度,我们引入了参数${\cal G}(L)=\langle \ln (V_{nm}/δ) \rangle$,它代表了局域算符$V$的典型矩阵元与能级间距$δ$的无序平均比;这个参数让人想起了单粒子局域化中的无扰电导。我们发现,参数${\cal G}(L)$减少系统的大小$L$在MBL阶段,并在各态历经阶段增长。我们推测,当${\cal G}(L)$与系统尺寸${\cal G}(L)={\cal G}_c\sim 1$无关时,会发生离域跃迁.我们通过研究多体局域化跃迁并使用精确对角化和时间演变块抽取方法求解无序1D XXZ自旋1/2链中的多体迁移率边缘来说明我们的方法。我们的标准MBL过渡的微观细节的过渡提供了见解。它的直接物理后果,特别是在过渡的物理慢输运,和广泛的纠缠熵的本征态,是符合最近的重整化群的预测。

英文摘要:

We propose a new approach to probing ergodicity and its breakdown in quantum many-body systems based on their response to a local perturbation. We study the distribution of matrix elements of a local operator between the system's eigenstates, finding a qualitatively different behaviour in the many-body localized (MBL) and ergodic phases. To characterize how strongly a local perturbation modifies the eigenstates, we introduce the parameter ${\cal G}(L)=\langle \ln (V_{nm}/δ) \rangle$, which represents a disorder-averaged ratio of a typical matrix element of a local operator $V$ to the energy level spacing, $δ$; this parameter is reminiscent of the Thouless conductance in the single-particle localization. We show that the parameter ${\cal G}(L)$ decreases with system size $L$ in the MBL phase, and grows in the ergodic phase. We surmise that the delocalization transition occurs when ${\cal G}(L)$ is independent of system size, ${\cal G}(L)={\cal G}_c\sim 1$. We illustrate our approach by studying the many-body localization transition and resolving the many-body mobility edge in a disordered 1D XXZ spin-1/2 chain using exact diagonalization and time-evolving block decimation methods. Our criterion for the MBL transition gives insights into microscopic details of transition. Its direct physical consequences, in particular logarithmically slow transport at the transition, and extensive entanglement entropy of the eigenstates, are consistent with recent renormalization group predictions.

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