Tunable hinge skin states in a hybrid skin-topological sonic crystal

Abstract: Higher-order topological states in sound have played a pivotal role in understanding the intricate physics underlying sound transport, giving rise to new strategy of manipulating sound. Here we report tunable structure for hinge skin states in a non-Hermitian acoustic metamaterial with hybrid skin-topological effect. Our finding shows that when on-site gain and loss are exquisitely introduced into acoustic topological insulators, chiral edge modes in Hermitian counterpart would respectively become amplified or attenuated at zigzag boundaries. If adjacent gain and loss boundaries are intentionally constructed, hinge skin states would take place at their intersections. By strategically combining non-Hermitian and topological physics, we successfully reveal how higher-order hinge modes originate from lower-order surface states and demonstrate flexible acoustic steering in tunable non-Hermitian blocks. Our findings unveil that skin-topological effect may hold significant applications in designing interesting acoustic devices with unconventional functions such as multidimensional acoustic control and accurate energy harvesting.