We explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems.
Broadband tuning of polarization states is pivotal yet challenging in modern photonics technologies, especially for miniaturized or integrated systems. Metasurfaces potentially provide an effective approach to resolve this challenge. However, once a metadevice is fabricated, its functionalities are determined, and it is hard to actively tune the polarization states. Here, the electrically tunable broadband polarization states by combining phase‐change material (vanadium dioxide) and dispersion‐free metasurface are demonstrated for the first time. The polarization states are modulated through the electrically driven, Joule‐heat‐induced phase transition of vanadium dioxide, where the output polarization state can be continuously tuned from horizontal one to vertical one, or from circular polarization to linear polarization. With accurate on‐chip control of the phase transition, continuous and reversible modulation of polarization is verified in a scanning display. Moreover, a proof‐of‐concept demonstration for dynamically independent control of multiple polarization display is carried out. Different images are produced by applying electrical currents in N separate channels to generate a dynamic multiplexing polarization display with 2N encoding states. Such an active metasurface can be readily integrated with electronics and has potential applications in display, encryption, camouflage, and information processing.
Most polarization-sensitive photodetectors detect either linearly polarized (LP) or circularly polarized (CP) light. Here, we experimentally demonstrate a multiple-polarization photodetector based on a hybrid organic–inorganic perovskite (HOIP) metasurface, which is sensitive to both LP and CP light simultaneously. The perovskite metasurface is composed of a HOIP antenna array on a single-crystal HOIP film. Owing to the antenna anisotropy, the absorption of linearly polarized light at the metasurface depends on the polarization angle; also, due to the mirror asymmetry of the antenna elements, the metasurface is also sensitive to different circular polarizations. Polarization-dependent photocurrent responses to both LP and CP light are detected. Our results highlight the potential of perovskite metasurfaces for integrated photoelectric applications.
The miniaturization and integration of optoelectronic devices require progressive size reduction of active layers, resulting in less optical absorption and lower quantum efficiency. In this work, we demonstrate that introducing a metasurface made of hybrid organic−inorganic perovskite (HOIP) can significantly enhance broadband absorption and improve photonto-electron conversion, which roots from exciting Mie resonances together with suppressing optical transmission. On the basis of the HOIP metasurface, a broadband photodetector has been fabricated where photocurrent boosts more than 10 times in the frequency ranging from ultraviolet to visible. The device response time is less than 5.1 μs at wavelengths 380, 532, and 710 nm, and the relevant 3 dB bandwidth is over 0.26 MHz. Moreover, this photodetector has been applied as a signal receiver for transmitting 2D color images in broadband optical communication. These results accentuate the practical applications of HOIP metasurfaces in novel optoelectronic devices for broadband optical communication.
The interplay between topology and correlation lies at the forefront of the modern condensed matter physics. In this work, we study the extended fermion-Hubbard model, including the onsite as well as the nearest-neighbor repulsive interactions, on a topological square lattice that supports the Chern insulator. Within the mean-field method, we find that the spontaneous symmetry breaking (SSB) charge density wave or antiferromagnetic insulator dominates the system when the onsite or NN interactions are strong enough. It is interesting that the antiferromagnetic Chern insulator will appear in the phase diagram when there is an explicitly nonvanishing sublattice potential. In addition, we explore how a finite-size ribbon structure affects the phase diagram and point out that the critical interaction for SSB occurs with weaker strength than the bulk system. arXiv:2001.06758v1 [cond-mat.str-el]
Hexagonal boron nitride supports phonon polaritons in its two Reststrahlen bands. In this paper, we investigate phonon polaritons in cylindrically curved hexagonal boron nitride thin films. The phonon polariton modes in such structure carry orbital angular momentums depending on its azimuthal index. For extremely small-size structures, high order polariton modes show cutoff behaviors; while, for large-size ones, modes with low azimuthal indexes are nearly degenerate, showing similar mode effective indexes. In dimer structures, phonon polariton modes in the neighboring structures are coupled, creating hybrid modes; gap phonon polaritons arise due to such coupling. For large-size dimers, multiple gap phonon polariton modes have been found. Then, cylindrically curved hexagonal boron nitride thin film is placed on a substrate, which also leads to the emergence of multiple gap phonon polariton modes near the touching point. In the end, we vary the geometric parameters of the structures and give some discussions about the phonon polariton modes. Based on these investigations, we may say that the curvature can strongly affect the phonon polariton modes in h-BN thin films.
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