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arXiv 2005.11812cond-mat.dis-nn
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多体定域态中出现的遍历行为

Emerging ergodic behavior within many-body localized states

Wai Pang Sze, Tai Kai Ng, Kam Tuen Law

摘要:

本文对一维自旋$1/2$ XXZ模型在随机在位纵向磁场$B_i$($-h\leq B_i\leq h$)中的能级间距统计进行了数值分析。我们集中在强无序极限$J_{\perp}<<J_z,h)$,其中$J_z$和$J_{\perp}$是(最近邻)自旋相互作用强度在$z$和平面($xy$)方向,分别。在此参数范围内,系统将处于多体定域(MBL)态。通过分析作为随机磁场强度$h$、多体态能量$E$、系统$M=\sum_i(s_i^z+{1\over2})$中自旋- $\uparrow$粒子数以及自旋相互作用强度$J_z$和$J_{\perp}$的函数的能级间距统计,我们证明了当$J_z\sim h$($N=$自旋链长度)。新兴的遍历阶段表现出质的不同的行为相比,通常的遍历阶段,存在于弱无序极限。

英文摘要:

We report in this paper our numerical analysis of energy level spacing statistics for the one-dimensional spin-$1/2$ XXZ model in random on-site longitudinal magnetic fields $B_i$ ($-h\leq B_i\leq h$)). We concentrate on the strong disorder limit $J_{\perp}<<J_z,h)$ where $J_z$ and $J_{\perp}$ are the (nearest neighbor) spin interaction strength in $z$- and planar ($xy$)- directions, respectively. The system is expected to be in a many-body localized (MBL) state in this parameter regime. By analyzing the energy-level spacing statistics as a function of strength of random magnetic field $h$, energy of the many-body state $E$, the number of spin-$\uparrow$ particles in the system $M=\sum_i(s_i^z+{1\over2})$ and the spin interaction strengths $J_z$ and $J_{\perp}$, we show that there exists a small parameter region $J_z\sim h$ where ergodic behaviour emerges at the middle of the many-body energy spectrum when $M\sim{N\over2}$ ($N=$ length of spin chain). The emerging ergodic phase shows qualitatively different behaviour compared with the usual ergodic phase that exists in the weak-disorder limit.

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