论文标题
Weyl节点Weyl Semimetal阶段中的Weyl节点的动态表征
Dynamical characterization of Weyl nodes in Floquet Weyl semimetal phases
论文作者
论文摘要
由于对非平衡(周期性驱动)拓扑问题的研究,现在可以理解,一些用于对物质平衡状态进行分类的拓扑不足不足以描述其非平衡对应物。的确,在浮标系统中,源自逆布鲁因区域的周期性引起的额外差距通常会导致没有平衡类似物的独特拓扑现象。在Floquet Weyl半学的背景下,可能在Quasienergy Zero和$π/T $($ t $的驾驶期)中诱导Weyl点,这两种类型的Weyl点可以在动量空间中彼此非常接近。由于它们的动量空间接近性,在理论和实验中,每个韦尔点的手性都可能很难表征,因此确定系统的整体拓扑结构使其具有挑战性。在这项工作中,我们提出了一个动态不变式的启发,我们提出了一个动力不变的,能够表征和区分不同的否定值下的Weyl点,从而在Floquet weyl samimetals的拓扑表征中进一步前进了一步。为了证明这种动态拓扑不变的有用性,我们考虑了表现出许多Weyl点的定期踢出Harper模型的变体(Floquet拓扑阶段的研究中的第一个模型),其中weyl点的数量无限地升高,并具有某些系统参数的强度。此外,我们研究了与Weyl点相关的两端运输特征。这项工作的理论发现为实验探测一些看似简单的Floquet半学系统的丰富拓扑带结构铺平了道路。
Due to studies in nonequilibrium (periodically-driven) topological matter, it is now understood that some topological invariants used to classify equilibrium states of matter do not suffice to describe their nonequilibrium counterparts. Indeed, in Floquet systems the additional gap arising from the periodicity of the quasienergy Brillouin zone often leads to unique topological phenomena without equilibrium analogues. In the context of Floquet Weyl semimetal, Weyl points may be induced at both quasienergy zero and $π/T$ ($T$ being the driving period) and these two types of Weyl points can be very close to each other in the momentum space. Because of their momentum-space proximity, the chirality of each individual Weyl point may become hard to characterize in both theory and experiments, thus making it challenging to determine the system's overall topology. In this work, inspired by the construction of dynamical winding numbers in Floquet Chern insulators, we propose a dynamical invariant capable of characterizing and distinguishing between Weyl points at different quasienergy values, thus advancing one step further in the topological characterization of Floquet Weyl semimetals. To demonstrate the usefulness of such a dynamical topological invariant, we consider a variant of the periodically kicked Harper model (the very first model in studies of Floquet topological phases) that exhibits many Weyl points, with the number of Weyl points rising unlimitedly with the strength of some system parameters. Furthermore, we investigate the two-terminal transport signature associated with the Weyl points. Theoretical findings of this work pave the way for experimentally probing the rich topological band structures of some seemingly simple Floquet semimetal systems.