低维关联量子系统的非平衡超快动力学过程研究

Recently, in the condensed matter physics community, sub-picosecond measurements have been proven to be a powerful and state-of-the-art?tool to study correlated materials. In such high time resolutions, which are typically less than the characteristic relaxation and dephasing time scales of the systems under studies, plenty of details of the degrees of freedom inside the systems can be reached. In consequence, not much surprisingly, many interesting phenomena have emerged, such as photoinduced phase transitions. The progress in experiments creates demands for theory to obtain the capacity to calculate efficiently the ultrafast nonequilibrium processes in correlated materials and to make relevant predictions. The challenge lies in the dual hardness of quantum fluctuations due to strong correlations and nonequilibrium. To address the issue, this project employs large-scale numerical simulations as main tools, to investigate the ultrafast nonequilibrium processes of low-dimensional correlated systems. In terms of numerical methods, we further develop and improve the time-dependent exact diagonalization and density-matrix renormalization group, in order to describe efficiently the systems' dynamics in time scales relevant to experiments. In physics, we aim in this way to look into the mechanisms of nonequilibrium phenomena of many-body systems when they are subjected to ultrafast stimuli.The final goal of the project is to establish the bridge step-by-step connecting model simulations to on-going experiments in this area, as well as to unearth novel nonequilibrium quantum phenomena originated from correlation effects.

近年来，亚皮秒分辨率下的光学探测和实验手段为凝聚态物理中关联材料的研究提供了新的强有力的工具，因为在小于系统弛豫和退相干特征时间的时间分辨率下获得的信息可以为人们提供关于系统内部自由度的大量细节。在这一时间尺度下发现了许多新的实验现象，例如光致诱导相变。这些实验进展对理论提出了挑战，要求能够对关联材料的超快非平衡演化进行有效的计算模拟和预言，而其所面临的核心困难是对关联量子涨落和非平衡的处理。本项目以大规模数值模拟为主要手段对低维量子关联系统的非平衡超快动力学过程进行研究。方法上，我们进一步发展含时精确对角化和密度矩阵重整化群，使其能够准确计算多自由度耦合的低维系统在实验相关的时间尺度下的动力学行为。从物理上，我们研究在超快外场激励下，多体系统非平衡演化的微观过程和机理。通过数值结果与实验的比较，逐步建立起模型计算和实验的直接联系，并探讨由于关联效应可能导致的新奇非平衡量子现象。

近年来，亚皮秒分辨率下的光学探测和实验手段为凝聚态物理中关联材料的研究提供了新的强有力的工具。以此为契机，本项目以大规模数值模拟为主要手段对低维量子关联系统的非平衡超快动力学过程进行研究。计划执行四年来，我们取得的主要进展如下：发展了可用于大规模并行计算的基于精确对角化的Lanczos含时演化算法；提出了数值上计算非平衡响应函数的pump-probe方法；在与其它方法相对照并建立联系的基础上，澄清了含时光电导计算中的一些误区和模糊之处；研究了一维扩展Hubbard模型在超快外场激励下的新物态，分析了隙间态的起源和物理内容，发现了另外一个利用非平衡手段实现相的调制和跨越的例子；结合实验结果，在模型计算的基础上，对掺杂的低维关联电子系统中的电荷自由度在超快外场激励后的弛豫和热化过程作了定量讨论，提出了支配电荷弛豫的两个比较普适的相互竞争的因素。项目执行期间，共计发表论文16篇，其中有项目基金标注的二区论文6篇。

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