Distinct electromagnetic properties can emerge from the three-dimensional (3D) configuration of a plasmonic nanostructure. Furthermore, the reconfiguration of a dynamic plasmonic nanostructure, driven by physical or chemical stimuli, may generate a tailored plasmonic response. In this work, we constructed a 3D reconfigurable plasmonic nanostructure with controllable, reversible conformational transformation using bottom-up DNA self-assembly. Three gold nanorods (AuNRs) were positioned onto a reconfigurable DNA origami tripod. The internanorod angle and distance were precisely tuned through operating the origami tripod by toehold-mediated strand displacement. The transduction of conformational change manifested into a controlled shift of the plasmonic resonance peak, which was studied by dark-field microscopy, and agrees well with electrodynamic calculations. This new 3D plasmonic nanostructure not only provides a method to study the plasmonic resonance of AuNRs at prescribed 3D conformations but also demonstrates that DNA origami can serve as a general self-assembly platform for constructing various 3D reconfigurable plasmonic nanostructures with customized optical properties.

We fabricate and experimentally characterize a broadband fractal acoustic metamaterial that can serve to attenuate the low-frequency sounds at selective frequencies ranging from 225 to 1175 Hz. The proposed metamaterials are constructed by the periodic Hilbert fractal elements made of photosensitive resin via 3D printing. In analogy to electromagnetic fractal structures, it is shown that multiple resonances can also be excited in the acoustic counterpart due to their self-similar properties, which help to attenuate the acoustic energy in a wide spectrum. The confinement of sound waves in such subwavelength element is evidenced by both numerical and experimental results. The proposed metamaterial may provide possible alternative for various applications such as the noise attenuation and the anechoic materials.

Acoustic metamaterials are artificial structures which can manipulate sound waves through their unconventional effective properties. Different from the locally resonant elements proposed in earlier studies, we propose an alternate route to realize acoustic metamaterials with both low loss and large refractive indices. We describe a new kind of acoustic metamaterial element with the fractal geometry. Due to the self-similar properties of the proposed structure, broadband acoustic responses may arise within a broad frequency range, making it a good candidate for a number of applications, such as super-resolution imaging and acoustic tunneling. A flat acoustic lens is designed and experimentally verified using this approach, showing excellent focusing abilities from 2 kHz and 5 kHz in the measured results.

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Strong coupling system with plasmons and emitters is an attractive field in the light-matter interaction for the hybrid states combined with the properties of plasmons and emitters. When the emitter are chiral molecules, surface plasmon polaritons (SPPs) provide an excellent research platform which possesses the advantages of chiral field enhancement and electromagnetic wave transmission in the subwavelength size and the chiral strong coupling system has wide applications in optical logic device and biological detection in nanoscale. We experimentally investigate the circular dichroism (CD) of the system with SPPs and chiral J-aggregates from the weak coupling regime to the strong coupling regime. The Rabi splitting of 143.3/154.5 meV, which is a significant phenomenon of the strong coupling can be observed both in the CD and the extinctions. Further experimental results show that, in the strong coupling regime, when the system achieves resonance, the intensity of CD signals corresponding to the upper energy band is stronger than that of the lower energy band, different from the behavior in the extinctions. We develop a method to calculate the dispersion relation in the chiral strong coupling system and explain the extinctions as well as the optical chirality of the hybrid states. The investigation of the CD enriches the characters of hybrid states in the strong coupling system and brings potential applications.