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Ebrahim I et al. i [3] investigate the temporal dynamics in strongly coupled ENZ plasmonic systems, illustrating the dynamics of field enhancement processes and highlighting the impact of dissipation loss. Beruete I et al. i [14] demonstrate experimentally the unusual waveguiding features of zero-permittivity structures with applications for enhanced sensing, and in parallel, Nicolussi I et al. i [15] discuss unusual unidirectional transparency in waveguides featuring zero-permittivity materials obeying parity-time symmetry. Zero-index metamaterials (photonic materials and artificial media with a near-zero refractive index in different parts of the electromagnetic spectrum) make possible novel forms of light-matter interactions where light behaves in a qualitatively different way than in conventional materials. [Extracted from the article]

Energy confinement plays an important role in improving wave–matter interactions, enabling applications such as sensing, lasing, and filtering. One convenient solution for achieving large energy-confinement is based on embedded eigenstates, i.e., non-radiating eigenmodes supported by open structures. While the analysis of these modes is quite consolidated in electromagnetics and optics, their relevance in acoustics has been less explored, despite their wide application potential. In this work, we explore acoustic embedded scattering eigenstates within the radiation continuum enabled by resonant metasurface pairs. At resonance, each metasurface strongly reflects the input wave, but as their surface resonances interfere with each other through coupling with a longitudinal resonance, an embedded eigenstate emerges. Through both theoretical and numerical analysis, we show the conditions for such an exotic resonant state to emerge and its implication for acoustic systems. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials and metasurfaces have been explored in the past few years to realize a wide range of extreme responses for sound waves. As one remarkable phenomenon, extreme anisotropy and hyperbolic sound propagation are particularly challenging to realize compared to electromagnetic waves because of the scalar nature of airborne acoustics. In parallel, moiré superlattices and the rapidly expanding domain of twistronics have shown that large anisotropy combined with tailored geometrical rotations can enable tantalizing emerging phenomena, such as tailored phase transitions in metamaterials. Connecting these areas of research, here, we explore the realization of acoustic hyperbolic metasurfaces and their combination to drive topological phase transitions from hyperbolic to elliptic sound propagation. The transition point occurring at a specific rotation angle between two acoustic metasurfaces supports highly directional canalization of sound, opening exciting opportunities for twisted acoustics metasurfaces for robust surface wave guiding and steering. [ABSTRACT FROM AUTHOR]

Here we present a roadmap on Photonic metasurfaces. This document consists of a number of perspective articles on different applications, challenge areas or technologies underlying photonic metasurfaces. Each perspective will introduce the topic, present a state of the art as well as give an insight into the future direction of the subfield. [ABSTRACT FROM AUTHOR]

This Special Topic collection provides an opportunity for the broad readership of Applied Physics Letters to get a glimpse of the recent advances in the area of metastructures and their applications. The main idea, borrowed from condensed matter physics, is that the nontrivial topological features of the band diagram of a metamaterial can be translated into an unusually robust boundary propagation of waves, of great interest for various applications from microwaves, photonics to acoustics. Huang I et al. i [32] as well as Mi I et al. i [36] and Zaccherini I et al. i [37] discuss various metamaterial geometries supporting broadband absorption exploiting sophisticated sound-matter interactions. The exotic wave phenomena in metastructures and their wide applications are one of the most researched subjects in electromagnetic waves and photonics, from radio frequencies to optics, and extend into several other disciplines, such as acoustics, mechanics, thermodynamics, materials science, condensed matter, etc. [Extracted from the article]

We investigate the use of a split-ring resonator (SRR) incorporated with an atomic-vapor cell to improve the sensitivity and the minimal detectable electric (E) field of Rydberg atom-based sensors. In this approach, a sub-wavelength SRR is placed around an atomic vapor-cell filled with cesium atoms for E-field measurements at 1.3 GHz. The SRR provides a factor of 100 in the enhancement of the E-field measurement sensitivity. Using electromagnetically induced transparency (EIT) with Aulter–Townes splitting, E-field measurements down to 5 mV/m are demonstrated with the SRR, while in the absence of the SRR, the minimal detectable field is 500 mV/m. We demonstrate that by combining EIT with a heterodyne Rydberg atom-based mixer approach, the SRR allows for a sensitivity of 5.5 μV/m Hz , which is two-orders of magnitude improvement in sensitivity than when the SRR is not used. [ABSTRACT FROM AUTHOR]