Abstract
Higher-order exceptional points have attracted increased attention in recent years due to their enhanced sensitivity and distinct topological features. Here, we show that non-local acoustic metagratings enabling precise and simultaneous control over their multiple orders of diffraction can serve as a robust platform for investigating higher-order exceptional points in free space. The proposed metagratings, not only could advance the fundamental research of arbitrary order exceptional points, but could also empower unconventional free-space wave manipulation for applications related to sensing and extremely asymmetrical wave control.
Highlights
Higher-order exceptional points have attracted increased attention in recent years due to their enhanced sensitivity and distinct topological features
Research in non-Hermitian wave physics showed that 2nd-order Exceptional points (EPs) can be realized by using two coupled cavities or waveguides, and such low-order EPs can be leveraged for sensing applications[18–20]
Extending this concept to higher-order EPs, is not trivial, since conventional metasurfaces do not offer precise and simultaneous control over the multiple propagating orders existing in the corresponding higher-order scattering matrices, which is instrumental for achieving higher-order EPs
Summary
Higher-order exceptional points have attracted increased attention in recent years due to their enhanced sensitivity and distinct topological features. We show that non-local acoustic metagratings enabling precise and simultaneous control over their multiple orders of diffraction can serve as a robust platform for investigating higher-order exceptional points in free space. EPs for open systems permitting wave propagation in higher-dimensions, on the other hand, would entail richer physics and offer a greater variety of wave functionalities Driven by these prospects, more recent studies have drawn inspiration from the progress in 2D wave functional materials[23–28] and shown that lossy acoustic metasurfaces[15,29–33] could serve as a fertile platform for engineering EPs. In particular, it was illustrated that a second-order EP derived from a 2 × 2 scattering matrix, which portrays a 2-channel metasurface, could give rise to extremely asymmetrical retro-reflection[30]. This is enabled by harnessing the non-local response of the constituent sub-units via evanescent wave fields, thereby offering the ability to efficiently mold the energy flow to multiple channels of reflection
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