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Abstract
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The judicious design of the electromagnetic boundary provides a crucial route to control light–matter interactions, and it is thus fundamental to basic science and practical applications. General design approaches rely on the manipulation of bulk properties of the superstrate or substrate and on the modification of boundary geometries. Due to the recent advent of metasurfaces and low-dimensional materials, the boundary can be flexibly featured with a surface conductivity, which can be rather complex but provide an extra degree of freedom to regulate the propagation of light. In this Perspective, we denote the boundary with a nonzero surface conductivity as the meta-boundary. The meta-boundaries are categorized into four types, namely, isotropic, anisotropic, biisotropic, and bianisotropic meta-boundaries, according to the electromagnetic boundary conditions. Accordingly, the latest developments for these four kinds of meta-boundaries are reviewed. Finally, an outlook on the research tendency of meta-boundaries is provided, particularly on the manipulation of light–matter interactions by simultaneously exploiting meta-boundaries and metamaterials.
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