[论文解读] Demonstration of Dynamic Topological Pumping Across Incommensurate Acoustic Meta-Crystals

Wenting Cheng, Emil Prodan+1 more|arXiv (Cornell University)|May 28, 2020

Topological Materials and Phenomena被引用 5

一句话总结

本研究通过可调谐相位自由度驱动绝热循环，在无外部同步的情况下，实现了非周期性声学超晶格中的自持动态拓扑泵浦。该系统实现了受控的、拓扑保护的边缘到边缘能量传输，仅在拓扑频率范围内可测量到信号，证实了经典可重构平台上拓扑边缘模式的鲁棒性。

ABSTRACT

A Thouless topological pump can be regarded as a dynamical version of the integer quantum Hall effect. In a finite configuration, a topological pump displays edge modes, which emerge dynamically from one bulk-band and dive into the opposite bulk-band, an effect that can be reproduced with both quantum and classical systems. In the classical setup, this phenomenon opens the possibility of controlled edge to edge energy transfer and many re-configurable meta-materials have been proposed for this purpose. However, driving them in real (as opposed to simulated) adiabatic cycles requires synchronized bulk deformations of the meta-material and this proved to be extremely challenging. Here, we report the first un-assisted dynamic energy transfer across a meta-material via pumping of topological edge modes. The system is a topological aperiodic acoustic meta-crystal, with a phason degree of freedom that is experimentally accessible and easily adjustable. As a result, the phason can be fast and periodically driven in adiabatic cycles, without any outside intervention or assistance. Furthermore, when one edge of the meta-crystal is excited in a topological forbidden range of frequencies, a microphone placed at the other edge starts to pick up signal as soon as the dynamic pumping process is set in motion. In contrast, the microphone picks no signal when the forbidden range of frequencies is non-topological.

研究动机与目标

• 实现一种无需对体变形进行外部同步控制的、经典的可重构系统，用于动态拓扑泵浦。
• 证明具有可调谐相位自由度的非周期性声学超晶格可自主支持绝热泵浦循环。
• 通过在受控频率激励下测量信号在边缘间的传播，验证真实物理系统中拓扑边缘模式的传输。
• 通过观察对侧边缘是否存在信号，区分拓扑与非拓扑频率范围。

提出的方法

• 利用具有可快速周期调制的相位自由度的非周期性声学超晶格。
• 实施快速、周期性的相位驱动，以在无外部协助或同步的情况下诱导绝热循环。
• 在超晶格的一个边缘施加处于拓扑禁带范围内的频率激励，以探测边缘模式的激发。
• 使用麦克风测量对侧边缘的信号检测，以确认动态能量传输。
• 比较拓扑与非拓扑频率范围下的信号响应，以分离出拓扑贡献。

实验结果

研究问题

• RQ1 是否可在无外部同步的、经典的非周期性声学超晶格中实现动态拓扑泵浦？
• RQ2 相位自由度是否能够实现适合拓扑泵浦的自主绝热循环？
• RQ3 在真实的实验装置中，是否可观测到拓扑保护的边缘到边缘能量传输？
• RQ4 对侧边缘的信号检测是否能够区分拓扑与非拓扑频率范围？

主要发现

• 该系统成功实现了通过拓扑边缘模式在超晶格中无外部同步的自持动态能量传输。
• 当激励频率处于拓扑禁带范围内时，对侧边缘的麦克风在动态泵浦过程启动后立即检测到信号。
• 当激励频率处于非拓扑范围时，对侧边缘未检测到信号，证实了边缘模式传输的拓扑保护特性。
• 相位自由度实现了系统在绝热循环中的快速周期性驱动，使泵浦过程无需外部干预即可完成。