声子晶体中的能谷态拓扑输运性质的理论与实验研究

Recently, a fast growing enthusiasm of studying the photonic version of topological insulators (TIs) was ignited due to the rich physics and attractive applications. In contrast, the sound analog of TIs receives much less attention, and the current studies stay mostly in a theoretical stage. One of our theoretical works [Lu & Qiu* et al., PRL 116, 093901 (2016)] states that, the degeneracy of a Dirac cone can be easily broken by rotating triangular scatterers. Interestingly, the degeneracy-lifted valley states exhibit a remarkable nature of vortex, associated with their vortex chirality determined by the orientations of the scatterers. This suggests a topological origin for such valley states. In this project, we will give a systemic study on the new kind of topological phononic crystals. For more details, we will unearth transport properties of bulk valley states from a perspective of topological protection, explore the possibility of edge states hosted in the boundary of different topological phases, and study the scattering problem of various impurities in bulk and edge systems. Based on precise full-wave simulations, we will establish a theoretical model to reveal the underlying physics, and verify the proposed topological transport properties in experiments finally. On the one hand, this investigation may stimulate a complete understanding between the classical and quantum TIs. On the other hand, such exotic topological transports can evoke extensive applications, e.g., in integrated acoustics and micro-particle manipulations.

最近，拓扑绝缘体以其丰富的物理内涵及诱人的应用前景，强烈激发了人们研究光子拓扑绝缘体的热情。相比之下，对声波拓扑绝缘体的探索则滞后很多，且主要停留在理论阶段。我们初步的理论研究表明[Lu & Qiu* etal.,PRL116,093901(2016)]，通过旋转三角形散射体可以巧妙地打开狄拉克锥简并；退简并的能谷态(valley states)具备明显的涡旋特征，且其手性和散射体的取向直接相关，这意味着这种能谷态具备某种拓扑起源。本项目拟将集中探讨这种新型的能谷态拓扑声子晶体。具体地，我们将从拓扑的角度深入研究各种体态输运性质，探索不同拓扑相之间的边界态存在的可能性，研究各类杂质对体态和边界态的散射问题等；在严格计算的基础上建立理论，最终实验证明相关输运现象。一方面，该研究可促成对经典、量子拓扑绝缘体的完备理解；一方面，这类新奇的拓扑输运性质可在集成声学、微颗粒声操控等领域获得广泛应用。

受凝聚态物理研究的启发，最近人们开始从对称性、能带拓扑分类等新视角深入理解声子晶体的带隙形成机制和通带传播特性，建立体态和边界态的密切关联。值得强调的是，声子晶体具有结构宏观、热力学（化学）稳定、容易调节和检测等优点，被视为实现、检验已有拓扑物理的优秀平台，也为发现全新的拓扑物态和拓扑性质提供可能。在本项目的资助下，我们理论提出并实验验证了一些极具声学特色的拓扑体系，观察到了一些独特的经典波拓扑输运现象。科学上，声子晶体拓扑物性研究可促成对经典、量子拓扑物态统一完备的理解，甚至领先于量子体系提出、发现一些有趣的拓扑物理效应和现象；应用上，这类基础研究可为研制性能卓越的新型声功能器件提供理论依据和知识储备。在本项目的支持下，共计发表学术论文19篇，其中14篇为通讯作者。以通讯或共同通讯作者身份发表的论文包括Nature 1篇；Nat. Phys. 2篇；PRL 3篇；Science Adv. 1篇；Nat. Commun. 1篇，PRB 2篇，PRE 1篇等。