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Recently, the advent of non-Hermitian topological systems—wherein energy is
not conserved—has sparked considerable theoretical advances. In particular, skin
effect and novel topological phases that can only exist in non-Hermitian systems
have been introduced. In all these phenomena the critical relation in open and
closed boundary condition for non-Hermitian one-dimensional chain is still under
speculation with immense curiosity. We will discuss the theoretical inventories
of such correspondences and demonstrate their experimental realizations in non-
Hermitian metamaterials. With quantum-to-classical analogy we create
mechanical metamaterials with non-reciprocal interactions to mimic non-
Hermiticity, in which our predicted open-closed or bulk-boundary
correspondence has been observed experimentally. It shows for a topological
chain, a change in the bulk corresponds to a change of localization of the
topological edge mode. Such unfamiliar bulk boundary correspondence has also
been manifested in the metamaterial to manipulate waves in unprecedented
fashions. These techniques are useful to engineer wave properties, steering waves
on demand, in sensing and energy harvesting. |