声子晶体中的表面声波赝自旋模式和拓扑保护声传输  

Pseudospin modes of surface acoustic wave and topologically protected sound transmission in phononic crystal

作　　者：王一鹤 张志旺 程营[1] 刘晓峻[1] Wang Yi-He;Zhang Zhi-Wang;Cheng Ying;Liu Xiao-Jun(Institute of Acoustics,School of Physics,Nanjing University,Nanjing 210093,China)

机构地区：[1]南京大学物理学院声学研究所

出　　处：《物理学报》2019年第22期258-265,共8页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2017YFA0303702);国家自然科学基金(批准号:119224071,11834008,11874215,11674172,11574148);江苏省自然科学基金(批准号:BK20160018)资助的课题~~

摘　　要：声子晶体中声表面波的调控在表面波应用方面有重要意义,拓扑声学理论为声子晶体表面波调控提供了新的思路.本文通过在硬质基板上排布蜂窝状晶格的空气圆柱孔阵列实现了结构表面局域的声表面波传播,并可在布里渊区K点上形成狄拉克锥.基于能带折叠理论构造复合胞,在复合胞布里渊区中心处实现了由二重简并偶极子态(p态)和四极子态(d态)组成的双狄拉克锥.通过扩大或缩小复合胞内相邻单元的间距,可以打开双狄拉克锥,将p态和d态分离,形成完全带隙.研究进一步发现,带隙附近声压场中声能流沿顺时针或逆时针方向转动,形成了表面声波的赝自旋态.复合胞内单元间距的缩小到扩大可导致能带反转,系统从平庸态转变为非平庸态,并伴随着拓扑相的变化.根据体态-边界态对应原则,构造了受拓扑保护的表面声波波导,实现了对声子晶体表面波的调控.The manipulation of surface acoustic wave(SAW)in phononic crystal plays an important role in the applications of SAW.The introduction of topological acoustic theory has opened a new field for SAW in phononic crystals.Here we construct pseudospin modes of SAW and topological phase transition along the surface of phononic crystal.The local SAW propagation is realized by air cylindrical holes in honeycomb lattice arranged on rigid substrate,and the Dirac cone is formed at the K point of the first Brillouin zone.Furthermore,using the band-folding theory,double Dirac cones can be formed at the center Гs point in the Brillouin zone of compound cell that contains six adjacent cylindrical air holes.The double Dirac cone can be broken to form two degenerated states and complete band gap by only shrinking or expanding the spacing of adjacent holes in the compound cell.It is found that the direction of energy is in a clockwise or counterclockwise direction,thus the pseudospin modes of SAW are constructed.The shrinkage-to-expansion of the compound cell leads to band inversion,and the system changes from trivial state to nontrivial state,accompanied by the phase transition.According to the bulk-boundary correspondence,the unidirectional acoustic edge states can be found at the interface between trivial system and nontrivial system.Then we can construct a topologically protected waveguide to realize the unidirectional transmission of surface waves without backscattering.This work provides a new possibility for manipulating the SAW propagating on the surface of phononic crystals and may be useful for making the acoustic functional devices based on SAW.

关 键 词：表面声波 双狄拉克锥 赝自旋 拓扑边界态 

分 类 号：TP3[自动化与计算机技术—计算机科学与技术]