image: IMAGE1: Bulk dispersions of the single layer and bilayer elastic metamaterials. a and b, Unit cell and bulk dispersion of the single layer elastic metamaterial. A quadratic degeneracy is preserved at the M point. The inset shows the first Brillouin zone. c and d, Unit cell and bulk dispersion of the bilayer elastic metamaterial. Chiral interlayer coupling is introduced by four tilted pillars, which opens a topologically nontrivial band gap (the grey region in d). In b and d, the colour maps represent the proportion of the out-of-plane displacement, and the black solid curves denote the fitting data of the effective Hamiltonians. Inset: the non-Abelian Wilson loop. view more
Credit: ©Science China Press
A collaboration between Prof. Weiying Deng at South China University of Technology, Prof. Feng Li at Beijing Institute of Technology, and Prof. Zhengyou Liu at Wuhan University was recently published online in National Science Review. There are growing interests on elastic waves manipulated by topological edge modes, which have unparallel advantages such as lower energy dissipation, higher flexibility and unidirectional transmission. However, whether an elastic metamaterial with time reversal symmetry and single topological phase can support topological edge modes on its own boundary is still an open question. By harnessing the full-vector feature of elastic waves, synthetic spin-orbital couplings were induced in a bilayer elastic metamaterial and thus give rise to the nontrivial topological band gap (IMAGE 1). They fabricated this elastic topological insulator by 3D metal-printed method, and further experimentally demonstrated the existence and back-scattering immune of the topological edge states (IMAGE 2). Finally, a heterostructure of the metamaterial that exhibits tunable edge transport was shown by tuning the height of the device.
The results may find potential applications in splitters and switches for elastic waves, and enable the construction of a monolithic elastic network. By stacking the structure layer-by-layer, this system can be extended to three dimensions with intriguing topological transports, such as robust surface states and higher-order hinge states.
Journal
National Science Review