Localized manipulation of spoof surface acoustic skyrmions with deep-subwavelength gradient structures

Skyrmions with stable vector field configurations have produced various derivatives with various topological textures, such as the Neel type, Bloch type, anti-type, and higher-order Neel type. Here, we theoretically and experimentally demonstrate that the vector field configuration of Neel-type skyrmionic modes can be locally manipulated using gradient grooves in a deep-subwavelength three-dimensional multilayer cylindrical structure. We experimentally observe that the skyrmionic modes can be contracted or expanded to manipulate the distribution of the velocity vectors by tuning the groove depth gradient along the structural radius, which is robust against structural deformations and defects. This type of controllable acoustic skyrmion provides new dimensions for advanced sound information processing, transportation, and data storage in compact structures.