ℤ ₂ Non‐Hermitian Skin Effect in Hermitian Topological Heterojunction Metamaterials

ABSTRACT The introduction of non‐Hermiticity has significantly broadened the research scope of topological physics and stimulated diverse potential applications. However, existing experimental works on non‐Hermitian (NH) phenomena predominantly rely on gain/loss or NH couplings. Here, we propose a Hermitian 2D heterojunction model without any NH terms, which comprises a ℤ 2 topological insulator interfaced with a conductor. The exchange of energy and particles on the 1D interface results in complex eigenenergies. Accompanied by time‐reversal symmetry, these complex energies induce a pair of skin modes that are exponentially localized at opposite boundaries of the interface, namely, the ℤ 2 NH skin effect. Remarkably, the non‐Hermiticity of the junction interface originates from the interplay between the ℤ 2 insulator and the conductor rather than explicit NH terms, enabling the experimental observation of ℤ 2 NH skin effect in passive circuit metamaterials. Such experimental configuration further suggests a direct translation to optical, acoustic, and other wave systems via the equivalent scattering properties between lumped circuit elements and waveguides. Our topological heterojunction provides a novel methodology for the implementation of non‐Hermiticity and establishes an alternative path for the design and application of NH effects.