声子晶体板中的第二类狄拉克点和边缘传输  

Type-Ⅱ Dirac points and edge transports in phononic crystal plates

作　　者：骆全斌 黄学勤 邓伟胤 吴迎 陆久阳 刘正猷[2] Luo Quan-Bin;Huang Xue-Qin;Deng Wei-Yin;Wu Ying;Lu Jiu-Yang;Liu Zheng-You(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,人工微纳结构教育部重点实验室,武汉430072

出　　处：《物理学报》2021年第18期197-203,共7页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11890701);广东省自然科学基金(批准号:2019B151502012,2021B1515020086,2021A1515010347);博士后科学基金(批准号:2020M672615)资助的课题.

摘　　要：在弹性板波体系中设计了一种具有第二类狄拉克点的声子晶体板.不同于第一类狄拉克点,第二类狄拉克点附近的色散具有大的倾斜,以致于等频面的几何形状由点状变成交叉的线状.微调结构的几何参数破缺该镜面对称性,可打开第二类狄拉克点简并,实现体系的能带反转.能带反转前后的二维声子晶体板属于不同的能谷拓扑相,不同拓扑相之间存在无带隙的拓扑保护界面态.不仅如此,由于弹性板波界面态的特殊应力分布,单一能谷相声子晶体板的边界上同样支持无带隙的弹性波传输.本文拓展类石墨烯体系中的二维狄拉克点和能谷态到第二类情形中,在同一结构中获得了界面和边界上的弹性波无带隙边缘传输.由于结构设计简单,可在微小尺寸下加工获得,为高频弹性波器件的设计和构造提供了可行的途径.The accidentally degenerate type-Ⅱ Dirac points in sonic crystal has been realized recently.However,elastic phononic crystals with type-Ⅱ Dirac points have not yet been explored.In this work,we design a two-dimensional phononic crystal plate in square lattice with type-Ⅱ Dirac points for elastic waves.The type-Ⅱ Dirac points,different from the type-Ⅰ counterparts,have the tiled dispersions and thus the iso-frequency contours become crossed lines.By tuning structures to break the mirror symmetry,the degeneracies of the type-Ⅱ Dirac points are lifted,leading to a band inversion.In order to have a further explanation,we also calculate the Berry curvatures of phononic crystals with opposite structure parameters,and it turns out that these two crystals hold opposite signs around the valley.The phononic crystal plates before and after the band inversion belong to different topological valley phases,whose direct consequence is that the topologically protected gapless interface states exist between two distinct topological phases.Topologically protected interface states are found by calculating the projected band structures of a supercell that contains two kinds of interfaces between two topological phases.Robustness of the interface transport is verified by comparing the transmission rate for perfect interface with that for defective interface.Moreover,owing to the special stress field distributions of the elastic plate waves,the boundaries of a single phononic crystal phase can similarly host the gapless boundary states,which is found by calculating the projected band structures of a supercell with a single phase,thus having two free boundaries on the edges.This paper extends the two-dimensional Dirac points and valley states in graphene-like systems to the type-Ⅱ cases,and obtains in the same structure the gapless interface and boundary propagations.Owing to the simple design scheme of the structure,the phononic crystal plates can be fabricated and scaled to a small size.Our system provides a feasible wa

关 键 词：声子晶体板 第二类狄拉克锥 弹性波 能带反转 

分 类 号：O735[理学—晶体学]