类弦动力学缺陷诱导的活性布朗振子中无色散平模与振动反常
Dispersionless Flat Mode and Vibrational Anomaly in Active Brownian Vibrators Induced by String-like Dynamical Defects
AI总结：
本研究在近二维双分散活性布朗振子系统中发现低能横向平模及振动态密度反常超额，证实类弦动力学缺陷是其微观起源，为理解活性物质集体行为提供了新机制。
摘要：
近年来，活性布朗粒子已成为理解活性物质行为的重要模型系统，其中粒子通过从周围环境获取能量实现自驱动运动。研究活性物质的核心目标是阐明其集体行为背后的物理机制。受分子玻璃领域研究进展的启发，本研究在活性布朗振子（一种近二维双分散颗粒组装体）的横向谱中发现了一种低能“平模”。我们证明，这种集体激发会导致振动态密度（VDOS）出现超出声子德拜贡献的反常超额。我们通过探究实验系统的参数空间，调控填充率、振动频率、粒径比和混合比，表征了该平模的特性。此外，我们通过经验证据证实，通过各粒子对约化横向VDOS贡献的空间分布识别出的类弦动力学缺陷，是该平模及其相关反常现象的微观起源。
英文摘要：
In recent years, active Brownian particles have emerged as a prominent model system for comprehending the behaviors of active matter, wherein particles demonstrate self-propelled motion by harnessing energy from the surrounding environment. A fundamental objective of studying active matter is to elucidate the physical mechanisms underlying its collective behaviors. Drawing inspiration from advancements in molecular glasses, our study unveils a low-energy ``flat mode" within the transverse spectrum of active Brownian vibrators -- a nearly two-dimensional, bi-disperse granular assembly. We demonstrate that this collective excitation induces an anomalous excess in the vibrational density of states (VDOS) beyond the phononic Debye contribution. We characterize the properties of this flat mode by exploring the parameter space of our experimental system and tuning the packing fraction, the vibrational frequency, the particle size ratio and the mixture ratio. Additionally, we establish through empirical evidence that string-like dynamical defects, discerned via the spatial distribution of each particle's contribution to the reduced transverse VDOS, serve as the microscopic origin of the flat mode and its associated anomalies.
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