Real-time and real-space spin and energy dynamics in one-dimensional spin-1/2 systems induced by local quantum quenches at finite temperatures
Real-time and real-space spin and energy dynamics in one-dimensional spin-1/2 systems induced by local quantum quenches at finite temperatures
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DOI：
10.1103/physrevb.89.075139
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发表时间：
2014-02-28
影响因子：
3.7
通讯作者：
Heidrich-Meisner, F.
中科院分区：
文献类型：
--
作者：
Karrasch, C.;Moore, J. E.;Heidrich-Meisner, F.
利用含时密度矩阵重整化群方法研究了有限温度下一维自旋为1/2的局域量子猝灭系统的自旋和能量动力学。选择足够大的系统尺寸，以确保可访问的时间尺度的时间相关数据代表热力学极限的行为。作为一个主要的结果，我们观察到的弹道传播的扰动的能量密度在可积自旋1/2 XXZ链的所有温度和交换各向异性，在这个模型中的发散热导率和准确的能量流守恒。相反，自旋动力学在无质量阶段是弹道的，但在易轴阶段的情况下，在背景自旋密度消失的情况下，在高温下表现出扩散行为。我们提取的自旋扩散常数的自旋密度的空间方差的时间依赖性，这与使用爱因斯坦关系从电流-电流相关函数得到的值吻合得很好的定量估计。有趣的是，扩散常数接近一个恒定值深易轴政权。作为不可积模型的一个例子，我们考虑两条腿的梯子，我们观察到的扩散能量和自旋动力学的迹象。我们的研究结果的相关性，最近的实验与量子磁体和玻色子的光学晶格进行了讨论。
We study the spin and energy dynamics in one-dimensional spin-1/2 systems induced by local quantum quenches at finite temperatures using a time-dependent density matrix renormalization group method. System sizes are chosen large enough to ensure that the time-dependent data for the accessible time scales represent the behavior in the thermodynamic limit. As a main result, we observe a ballistic spreading of perturbations of the energy density in the integrable spin-1/2 XXZ chain for all temperatures and exchange anisotropies, related to the divergent thermal conductivity in this model and the exact conservation of the energy current. In contrast, the spin dynamics is ballistic in the massless phase, but shows a diffusive behavior at high temperatures in the easy-axis phase in the case of a vanishing background spin density. We extract a quantitative estimate for the spin-diffusion constant from the time dependence of the spatial variance of the spin density, which agrees well with values obtained from current-current correlation functions using an Einstein relation. Interestingly, the diffusion constant approaches a constant value deep in the easy-axis regime. As an example for nonintegrable models, we consider two-leg ladders, for which we observe indications of diffusive energy and spin dynamics. The relevance of our results for recent experiments with quantum magnets and bosons in optical lattices is discussed.