Second-order elastic topological insulator with valley-selective corner states

Second-order elastic topological insulators (SETIs) with topologically protected corner states offer new routes for the realization of the robust manipulation of elastic waves in lower dimensions, providing the unprecedented ways for integrated ultrasound sensors and energy harvesting devices. However, traditional SETIs lack the flexibility of turning on and off the corner states on demand. Herein, we proposed a type of SETIs possessing the valley-selective topological corner states, endowing the capability of activating corner states by engineering the valley positions. An extra type of corner states with anti-symmetric displacement profile is also observed in the proposed SETIs, which is attributed to the enhanced long-range effect. The discrete mechanical model is firstly investigated and then expanded into the PC plate, in which the theory of Wannier center can well elucidate the corner states with valley-selectivity. The experimental results validate the existing corner states with valley-selectivity and anti-symmetric displacement profile. The proposed discrete model acts as a versatile platform presenting the relevant topological effects. The achieved valley-selectivity and multi-polarization features hosted in the designed SETI may contribute to their practicality and reconfigurability in elastic energy trapping, detecting, and harvesting device.