赝自旋-轨道耦合诱导的声自旋陈数拓扑绝缘体  

Spin-Chern insulator induced by pseudospin-orbit coupling in phononic crystals

作　　者：邓伟胤 黄学勤 陆久阳 刘正猷[2] DENG WeiYin;HUANG XueQin;LU JiuYang;LIU ZhengYou(School of Physics and Optoelectronics,South China University of Technology,Guangzhou 510640,China;Key Laboratory of Artificial Micro-and Nanostructures of Ministry of Education and School of Physics and Technology,Wuhan University,Wuhan 430072,China)

机构地区：[1]华南理工大学物理与光电学院,广州510640 [2]武汉大学物理科学与技术学院和教育部人工微纳结构重点实验室,武汉430072

出　　处：《中国科学：物理学、力学、天文学》2021年第8期107-112,共6页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家自然科学基金(编号:11890701,11774275,11974120,11974005,12074128)资助项目。

摘　　要：受拓扑保护的经典波边界模式对稳健的能量传输和可靠的信息处理有重要的意义.以往声波的拓扑边界模式,主要是在能带反转的两个声子晶体相之间的界面上实现,即表现为界面态.本工作通过构造由赝自旋-轨道耦合诱导的二维拓扑声子晶体,在单一声子晶体相的边缘上(即表面上)即获得了无带隙的螺旋性边界态.该边界态起源于非平庸的体拓扑,由自旋陈数描述,因此该声子晶体被称为声自旋陈数拓扑绝缘体.实验证明了这些边界态的存在.特别是,由于体系打破了赝自旋守恒,实验中观察到边界态的赝自旋翻转现象.The boundary modes of classical waves protected by the topology are of great significance for robust energy transmission and reliable information processing. Many endeavors have been made to realize topological insulators in electromagnetic, mechanical and acoustic systems. Previous studies on acoustic boundary modes mainly focused on the interface states at the domain walls between different topological phases of phononic crystals. In electromagnetic and mechanical systems, although helical boundary states have been observed, the pseudospin in them is conserved, thus these systems can be considered as two independent copies of Chern insulators. When the pseudospin conservation is broken, the topology cannot be described by Chern numbers, and the spin will vary in transport. This general case remains to be explored both in electronic and classical systems. In this work, we constructed a two-dimensional topological phononic crystal induced by pseudospin-orbit coupling, which hosts the gapless helical boundary modes at the edge of a phononic crystal. Since these boundary states originate from non-zero spin-Chern numbers, the system is called the spin-Chern insulator. We have observed these boundary states in experiments, and observed the spin-flipping transport in the H-shaped sample, proving the spin non-conservation of the boundary states. Different from the earlier work, this work demonstrates two important aspects: first, the acoustic topological insulator is induced by the pseudospin-orbit coupling, and possesses the gapless helical edge states on its boundary, thus is the first analogue of topological insulator for acoustic wave;second, the inherent spin conservation is broken, which expands and deepens the knowledge of current topological physics in classical and electronic systems. The helical boundary states may have potential applications in new topological acoustic devices.

关 键 词：声子晶体 拓扑绝缘体 自旋-轨道耦合 自旋陈数 

分 类 号：O469[理学—凝聚态物理]