近日，苏州大学的蒋建华及其研究小组与美国福坦莫大学的Camelia Prodan以及美国叶史瓦大学的Emil Prodan等人合作并取得一项新进展。经过不懈努力，他们成功观察到声学超材料中的D类拓扑。相关研究成果已于2024年2月1日在国际知名学术期刊《科学通报》上发表。

本文采用了一种新颖的设计方案，成功地在声学晶体中实现了二维拓扑D类相。该方案通过在宽频率范围内合成粒子-空穴和类费米子时间反演对称性，利用具有实值耦合的富集晶胞结构，模拟了具有复杂跳跃的拓扑D类相的目标哈密顿量。这一技术为所有无源超材料拓扑类的实现提供了可能。在实验中，研究人员在两个独立的扇区中实现了具有相反Chern数的拓扑D类相，这两个扇区通过系统中建立的类费米子的时间反演对称性连接起来。

他们还测量了声学马约拉纳类螺旋边缘模式，并观察到了其鲁棒拓扑输运现象，为D和DIII类拓扑提供了直接证据。这项研究为两类基本拓扑相的实验实现开辟了新的途径，对基础物理、材料科学和声子信息处理等领域提供了新的见解。

据悉，拓扑材料和超材料为生成和操纵具有非常规性质的物质相开辟了新的范式。拓扑D类相（TDP）是具有粒子-空穴对称的十重分类拓扑相的原型，在二维中支持传播拓扑边缘模式，模拟难以捉摸的马约拉纳基本粒子。此外，在TDP中刺穿π通量狄拉克螺线管可以稳定局部马约拉纳激发，用于拓扑量子计算。尽管二维（2D）拓扑D类相已成为研究前沿的焦点，其实验实现仍存在争议。

附：英文原文

Title: Observation of D-class topology in an acoustic metamaterial

Author: Shi-Qiao Wu, Wenting Cheng, Xiao-Yu Liu, Bing-Quan Wu, Emil Prodan, Camelia Prodan, Jian-Hua Jiang

Issue&Volume: 2024/02/01

Abstract: Topological materials and metamaterials opened new paradigms to create and manipulate phases of matter with unconventional properties. Topological D-class phases (TDPs) are archetypes of the ten-fold classification of topological phases with particle-hole symmetry. In two dimensions, TDPs support propagating topological edge modes that simulate the elusive Majorana elementary particles. Furthermore, a piercing of π-flux Dirac-solenoids in TDPs stabilizes localized Majorana excitations that can be braided for the purpose of topological quantum computation. Such two-dimensional (2D) TDPs have been a focus in the research frontier, but their experimental realizations are still under debate. Here, with a novel design scheme, we realize 2D TDPs in an acoustic crystal by synthesizing both the particle-hole and fermion-like time reversal symmetries for a wide range of frequencies. The design scheme leverages an enriched unit cell structure with real-valued couplings that emulate the targeted Hamiltonian of TDPs with complex hoppings: A technique that could unlock the realization of all topological classes with passive metamaterials. In our experiments, we realize a pair of TDPs with opposite Chern numbers in two independent sectors that are connected by an intrinsic fermion-like time-reversal symmetry built in the system. We measure the acoustic Majorana-like helical edge modes and visualize their robust topological transport, thus revealing the unprecedented D and DIII class topologies with direct evidence. Our study opens up a new pathway for the experimental realization of two fundamental classes of topological phases and may offer new insights in fundamental physics, materials science, and phononic information processing.

DOI: 10.1016/j.scib.2024.01.041

Source: https://www.sciencedirect.com/science/article/abs/pii/S2095927324000689