Electric control of coupling in hybrid graphene/metamaterial system enables strong selective modulation of light polarization.

physics, it is still a big challenge to achieve practical metamaterials for real-world applications-primarily due to their bulky size, unavoidable material losses, and fabrication difficulties. Metasurfaces, 2D counterparts of metamaterials that consist of 2D array of planar metallic or dielectric structures, have shown great promise for practical applications owing to their exceptional capability of controlling the wavefront of light. [17][18][19][20] With suitable design of the building blocks, metasurfaces are capable of generating phase discontinuities with in-plane gradient, leading to anomalously refracted beam in transmission and/or reflection. Recent progress in metasurfaces has led to various ultrathin optical devices including flat lenses, [21][22][23][24] vortex beam generators, [23][24][25] broadband quarter wave plates, [26,27] efficient surface plasmon couplers, [28] 3D and high-efficiency holograms. [29][30][31][32] The concept of metasurfaces has also been extended to nonlinear optics for manipulating the nonlinearity phase in harmonic generations. [33,34] Although metasurfaces have offered new degrees of freedom for controlling the propagation of light, the amplitude of anomalous refracted waves in metasurfaces is typically fixed by their structural geometry and dimensions, which limits their potential for various applications that require dynamical control over the electromagnetic waves, such as active focusing for lensing and dynamic holography. Active tuning of metasurface requires incorporation of active media whose electromagnetic properties can be changed in real time under external stimuli. Recently, it was shown that anomalous deflection can be dynamically controlled by means of various tuning schemes based on microelectromechanical system (MEMS) [35] and Schottky diode. [36] One suitable candidate for such purpose is graphene, a 2D form of carbon with the atoms arranged in a honeycomb lattice. Graphene has been studied extensively during the last decade due to its high carrier mobility and unique doping capability originated from its gapless and cone-shaped band structure at the Dirac point. Graphene also shows a gate-controllable lightmatter interaction by the shift of the Fermi level, which can be further enhanced by the electromagnetic resonance provided by suitably designed structures. [37,38] Particularly, in the terahertz (THz) regime, strong modulation has been achieved by electrically tuning the density of states available for intraband transitions. [39] Although significant effort has been devoted to various graphene-based metamaterials for active control of the amplitude and polarization of THz waves in direct transmission, [40][41][42][43] Although recent progress in metasurfaces has shown great promise for applications, optical properties in metasurfaces are typically fixed by their structural geometry and dimensions. Here, an electrically controllable amplitude of anomalously-refracted waves in a hybrid graphene/metasurface system are experimentally demonstrated, which cons...

Memory metamaterials are artificial media that sustain transformed electromagnetic properties without persistent external stimuli. Previous memory metamaterials were realized with phase-change materials, such as vanadium dioxide or chalcogenide glasses, which exhibit memory behaviour with respect to electrically/optically induced thermal stimuli. However, they require a thermally isolated environment for longer retention or strong optical pump for phase-change. Here we demonstrate electrically programmable nonvolatile memory metadevices realised by the hybridization of graphene, a ferroelectric and meta-atoms/meta-molecules, and extend the concept further to establish reconfigurable logic-gate metadevices. For a memory metadevice having a single electrical input, amplitude, phase and even the polarization multi-states were clearly distinguishable with a retention time of over 10 years at room temperature. Furthermore, logic-gate functionalities were demonstrated with reconfigurable logic-gate metadevices having two electrical inputs, with each connected to separate ferroelectric layers that act as the multi-level controller for the doping level of the sandwiched graphene layer.

Extreme optical properties can be realized by the strong resonant response of metamaterials consisting of subwavelength-scale metallic resonators. However, highly dispersive optical properties resulting from strong resonances have impeded the broadband operation required for frequency-independent optical components or devices. Here we demonstrate that strong, flat broadband optical activity with high transparency can be obtained with meshed helical metamaterials in which metallic helical structures are networked and arranged to have fourfold rotational symmetry around the propagation axis. This nondispersive optical activity originates from the Drude-like response as well as the fourfold rotational symmetry of the meshed helical metamaterials. The theoretical concept is validated in a microwave experiment in which flat broadband optical activity with a designed magnitude of 45°per layer of metamaterial is measured. The broadband capabilities of chiral metamaterials may provide opportunities in the design of various broadband optical systems and applications.

However, dislocations, disinclinations, and symmetry-breaking instabilities can frequently prompt the formations of defects and grain boundaries in the synthesis processes [15,16] and crystal growth rate of the 2D nanostructure is very slow. [17,18] In nature system, organic-inorganic hybrid nanostructures with high-crystallinity and diverse morphologies can be constructed by biomineralization process. [19,20] This natural process can efficiently induce the molecular rearrangement for high complexity [21] and many functionalities. [22,23] Therefore, these unique biological phenomena have been applied in synthesis method to control the crystallinity and morphology of 2D nanostructures with superior material properties. Here, we show a solution-based ultrafast 2D growth method for large-scale and high-quality silver nanosheets on air/gel interface. The biological hydrogel polymer forms a multilayered structure by a solvent-induced phase separation process at air/gel interface with trapped silver (Ag) salts between the layers. [24] Furthermore, the trapped Ag salts between each biological hydrogel layers can efficiently reduce into large-scale 2D Ag nanosheets during the annealing process.The mixture of the Ag salts and hydrogel solution is a transparent, light yellow color at room temperature with reduced viscosity as compared with pure gelatin solution (Figure S1a, Supporting Information), while its nominal phase-change temperature is 154 °C based on the thermal gravimetric analysis (TGA) analysis results ( Figure S1b, Supporting Information). The viscosity of the hydrogel mixture decreases further at above 40 °C as the hydrogen bond in the triple-helix gelatin chain [25] degrades by the intercalation of Ag ions between various functional side chains (e.g., amine, carboxyl, hydroxyl, and thiolate groups). [26] Adding methyl alcohol and Ag salts in the solution can partially neutralize and condense the hydrogel polymer chains [24,27] to form large and continuous multilayer membranes via the salting-out effect ( Figure S2, Supporting Information). Conceptually, Ag ions are coordinated on the randomly coiled gelatin chains, which are rapidly accumulated under elevated temperature to form a multi layered structure (Figure 1a). [28] The neutralization and condensation process occurs, and the Ag ions are trapped between the layers of the hydrogel scaffold (Figure 1b). A reducing agent, dopamine, is used to promote the conversion of Ag ions to atoms while large, multilayered gelatin scaffolds constrain the crystallization process laterally to increase the The growth of large and high-quality 2D nanomaterials is challenging due to the formation of defects from dislocations, disinclinations, and symmetrybreaking instabilities. In this study it is demonstrated that biological template can be utilized to align the molecular orientation for large grain size in the synthesis of the high-quality 2D silver nanostructure. The solvent assisted multilayering phenomenon of hydrogel forms biological template at the air/ gel interface...

Malfunctions at the site of neuromuscular junction (NMJ) of post-injuries or diseases are major barriers to recovery of function. The ability to efficiently derive motor neurons (MN) from embryonic stem cells has indicated promise toward the development of new therapies in increasing functional outcomes post injury. Recent advances in micro-technologies have provided advanced culture platforms allowing compartmentalization of sub-cellular components of neurons. In this study, we combined these advances in science and technology to develop a compartmentalized in vitro NMJ model. The developed NMJ system is between mouse embryonic stem cell (mESC)-derived MNs and c2c12 myotubes cultured in a compartmentalized polydimethylsiloxane (PDMS) microfluidic device. While some functional in vitro NMJ systems have been reported, this system would further contribute to research in NMJ-related diseases by providing a system to study the site of action of NMJ aimed at improving promoting better functional recovery.

Chirality is a universal feature in nature, as observed in fermion interactions and DNA helicity. Much attention has been given to chiral interactions of light, not only regarding its physical interpretation but also focusing on intriguing phenomena in excitation, absorption, refraction, and topological phase. Although recent progress in metamaterials has spurred artificial engineering of chirality, most approaches are founded on the same principle of the mixing of electric and magnetic responses. Here we propose nonmagnetic chiral interactions of light based on low-dimensional eigensystems. Exploiting the mixing of amplifying and decaying electric modes in a complex material, the lowdimensionality in polarization space having a chiral eigenstate is realized, in contrast to 2-dimensional eigensystems in previous approaches. The existence of optical spin black hole from low-dimensional chirality is predicted, and singular interactions between chiral waves are confirmed experimentally in parity-time-symmetric metamaterials.

Extraordinary properties of traditional hyperbolic metamaterials, not found in nature, arise from their man-made subwavelength structures causing unique light−matter interactions. However, their preparation requiring nanofabrication processes is highly challenging and merely provides nanoscale two-dimensional structures. Stabilizing their bulk forms via scalable procedures has been a sought-goal for broad applications of this technology. Herein, we report a new strategy of designing and realizing bulk metamaterials with finely tunable hyperbolic responses. We develop a facile two-step process: (1) self-assembly to obtain heterostructured nanohybrids of building blocks and (2) consolidation to convert nanohybrid powders to dense bulk pellets. Our samples have centimeter-scale dimensions typically, readily further scalable. Importantly, the thickness of building blocks and their relative concentration in bulk materials serve as a delicate means of controlling hyperbolic responses. The resulting new bulk heterostructured material system consists of the alternating h-BN and graphite/graphene nanolayers and exhibits significant modulation in both type-I and type-II hyperbolic resonance modes. It is the first example of real bulk hyperbolic metamaterials, consequently displaying the capability of tuning their responses along both in-plane and out-of-plane directions of the materials for the first time. It also distinctly interacts with unpolarized and polarized transverse magnetic and electronic beams to give unique hyperbolic responses. Our achievement can be a new platform to create various bulk metamaterials without complicated nanofabrication techniques. Our facile synthesis method using common laboratory techniques can open doors to broad-range researchers for active interdisciplinary studies for this otherwise hardly accessible technology.