Hybrid-Order Skin Effect from Loss-Induced Nonreciprocity
Jien Wu, Yejian Hu, Zhaojian He, Ke Deng, Xueqin Huang, Manzhu Ke, Weiyin Deng, Jiuyang Lu, Zhengyou Liu
Abstract
Skin effects, the phenomena of the bulk states collapsing toward open boundaries, have mostly been revealed in non-Hermitian systems hosting nonreciprocity. Either the first-order or the higher-order of skin effects have been observed. Here, we report our first discovery of a hybrid-order of skin effects, of which the utilized two-dimensional system exhibits not only the first-order skin modes, but also the second-order skin modes respectively on the edges and the corners, the different type of open boundaries. We propose a universal approach to achieving nonreciprocal couplings by virtue of the loss and bilayer degree of freedom, as the critical role it plays. Our models are implemented in square- and diamond-shaped phononic crystals, and the hybrid order of acoustic skin modes is evidenced in experiment. Our Letter may foster the development of non-Hermitian physics.