Phonon Polaritons in Twisted Double-Layers of Hyperbolic van der Waals Crystals

Zheng, Zebo; Sun, Fengsheng; Huang, Wuchao; Jiang, Jingyao; Zhan, Runze; Ke, Yu; Chen, Huanjun; Deng, Shaozhi

doi:10.1021/acs.nanolett.0c01627

Cited by 143 publications

(119 citation statements)

References 40 publications

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“…Several samples with increasing rotation angles were fabricated, confirming hyperbolic-to-elliptic topological transitions, both reflected in the mapped near-field distribution (left, Figure 7F) and the obtained dispersion (right, Figure 7F) [25]. These results were also confirmed by other experiments [110,111]. Extreme dispersion engineering may stimulate new research in the field of 'opto-twistronics', based on stacking tBLs and multilayer polaritonic surfaces, with the opportunity for extreme light manipulation at the nanoscale based on a simple geometrical rotation.…”

Section: Direct Writing Photolithography Assemblysupporting

confidence: 80%

Tailoring Light with Layered and Moiré Metasurfaces

Wang

Mazor

et al. 2021

Trends in Chemistry

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Optical metasurfaces are assemblies of subwavelength, artificially designed inclusions forming planarized devices with unprecedented capabilities to manipulate electromagnetic waves and facilitate multiple functionalities. Recent topical efforts in this research area have been focused on pushing forward the frontiers of enhanced light-matter interactions exploiting new concepts and fabrication capabilities. In this context, layered and twisted metasurfaces have showcased interesting features, including flexibility and tunability in manipulating light, contributing to the development of moiré physics for light. Here, we provide an overview on the state-of-art layered and stacked moiré metasurfaces. Freespace multifunctional metadevices are first discussed, followed by recent discoveries in polaritonics and twistronics for twisted hyperbolic metasurface bilayers. We conclude with a discussion on recent advances in the nanofabrication of moiré metasurfaces and remark on their future potential applications. Emerging Strategies for Advanced Optical Metasurfaces Using Twisting and StackingOptical metasurfaces (see Glossary), commonly recognized as the 2D counterpart of bulk metamaterials, are composed of subwavelength planarized inclusions [1,2]. Unlike metamaterials, metasurfaces usually have a thickness smaller than the operational wavelength in free space, holding the promise for next-generation multifunctional, compact, and integrated functional optical devices. Their ultrathin nature can significantly ease nanofabrication requirements compared with metamaterials, making them compatible for mass production in the semiconductor industry. One essential step in designing metasurfaces is to control light interactions with its local functional composites, so-called meta-atoms, thus enabling unprecedented control of the local scattering processes in terms of phase, amplitude, polarization, frequency, dispersion, and more [3][4][5][6]. In this way, a designer metasurface can be endowed with unprecedented control in tailoring the impinging light. This process inherently requires resonant light-matter interactions in meta-atoms, given the small light-matter interaction length. Tremendous efforts have been made in searching for better materials and novel metasurface designs for improved performance. For composite materials, metals can support enhanced photonic local density of states due to plasmonic phenomena, but may suffer from large Ohmic loss [7][8][9]. On the contrary, all-dielectric materials have significantly lower loss, but typically require a larger thickness, in the order of the wavelength in the material, limiting the field localization and enhancement of light-matter interactions [10]. Various geometries have been explored to realize metasurfaces, including split ring resonators, nanorods, and V-shape nanoantennas, supporting optical resonances in subwavelength meta-atoms [7,10]. These designs typically rely on heavy optimization techniques to obtain the best responses, requiring computational resources and tim...

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Section: Direct Writing Photolithography Assemblysupporting

confidence: 80%

Tailoring Light with Layered and Moiré Metasurfaces

Wang

Mazor

et al. 2021

Trends in Chemistry

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“…The polaritonic iso‐frequency curves (IFCs, slices of the dispersion surface in frequency‐momentum space by a plane of a constant frequency ν) are described by open hyperbolas, giving rise to exotic and very intriguing optical phenomena, such as extremely high momenta [ 8 ] (as needed for electromagnetic field confinement), small group velocities, negative phase velocities [ 9 ] (with great potential for applications exploiting negative refraction and Doppler effects at the nanoscale [ 10,11 ] ), ultralong lifetimes, [ 3,12 ] and more recently, flat‐band canalization of topological polaritons in twisted vdW bilayers. [ 13–16 ]…”

Section: Figurementioning

confidence: 99%

Nanoscale‐Confined Terahertz Polaritons in a van der Waals Crystal

et al. 2020

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Electromagnetic field confinement is crucial for nanophotonic technologies, since it allows for enhancing light–matter interactions, thus enabling light manipulation in deep sub‐wavelength scales. In the terahertz (THz) spectral range, radiation confinement is conventionally achieved with specially designed metallic structures—such as antennas or nanoslits—with large footprints due to the rather long wavelengths of THz radiation. In this context, phonon polaritons—light coupled to lattice vibrations—in van der Waals (vdW) crystals have emerged as a promising solution for controlling light beyond the diffraction limit, as they feature extreme field confinements and low optical losses. However, experimental demonstration of nanoscale‐confined phonon polaritons at THz frequencies has so far remained elusive. Here, it is provided by employing scattering‐type scanning near‐field optical microscopy combined with a free‐electron laser to reveal a range of low‐loss polaritonic excitations at frequencies from 8 to 12 THz in the vdW semiconductor α‐MoO3. In this study, THz polaritons are visualized with: i) in‐plane hyperbolic dispersion, ii) extreme nanoscale field confinement (below λo ⁄75), and iii) long polariton lifetimes, with a lower limit of >2 ps.

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“…Exploring these unusual phenomena is central in the developing field of quantum twistronics 4 , 5 . The concept of twistronics has been extended to include the study of nano-light properties in materials like TBG and twisted α -MoO 3 6 – 9 . Recently, it was shown that applying the ideas of twistronics to both 1D and 2D photonic moiré lattices in dielectric nanophotonic materials leads to slow-light effect 10 , 11 , light localization/delocalization phenomena 12 , and tunable resonant chiral behavior 13 .…”

Section: Introductionmentioning

confidence: 99%

Modeling the optical properties of twisted bilayer photonic crystals

Tang

Carr

et al. 2021

Light Sci Appl

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We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow-light behavior. Our twisted bilayer photonic device, which has an operating wavelength in the C-band of the telecom window, uses two crystalline silicon photonic crystal slabs separated by a methyl methacrylate tunneling layer. We numerically determine the magic angle using a finite-element method and the corresponding photonic band structure, which exhibits a flat band over the entire Brillouin zone. This flat band causes the group velocity to approach zero and introduces light localization, which enhances the electromagnetic field at the expense of bandwidth. Using our original plane-wave continuum model, we find that the photonic system has a larger band asymmetry. The band structure can easily be engineered by adjusting the device geometry, giving significant freedom in the design of devices. Our work provides a fundamental understanding of the photonic properties of twisted bilayer photonic crystals and opens the door to the nanoscale-based enhancement of nonlinear effects.

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Phonon Polaritons in Twisted Double-Layers of Hyperbolic van der Waals Crystals

Cited by 143 publications

References 40 publications

Tailoring Light with Layered and Moiré Metasurfaces

Tailoring Light with Layered and Moiré Metasurfaces

Nanoscale‐Confined Terahertz Polaritons in a van der Waals Crystal

Modeling the optical properties of twisted bilayer photonic crystals

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