By engineering the arrangement of these nanoscale unit cells into a desired architecture or geometry, one can tune the refractive index of the metamaterial to positive, near-zero or negative values. These structural units-the constituent artificial ‘atoms’ and ‘molecules’ of the metamaterial-can be tailored in shape and size, the lattice constant and interatomic interaction can be artificially tuned, and ‘defects’ can be designed and placed at desired locations. The core concept of metamaterial design is to craft materials by using artificially designed and fabricated structural units to achieve the desired properties and functionalities. This review discusses these metamaterials and metasurfaces from the perspectives of materials, mechanisms and advanced metadevices in depth, with the aim to serve as a solid reference for future works in this exciting and rapidly emerging topic. Such configurations are impacting the electromagnetic light waves to generate novel properties that are difficult or even impossible to obtain with natural materials. Metamaterial’s nanostructures have precise shape, geometry, size, direction and arrangement. Metamaterials and functional material development strategies are focused on the structures of the matter itself, which has led to unconventional and unique electromagnetic properties through the manipulation of light-and in a more general picture the electromagnetic waves-in widespread manner. ![]() Photonic crystals, nanolithography, plasmonics phenomena and nanoparticle manipulation are the main areas where these techniques have been applied successfully and led to an emergent material sciences branch known as metamaterials. At the nanoscale, to control light and heat, matured nanostructure fabrication techniques have been developed in the last two decades, and a wide range of groundbreaking processes have been achieved. Wireless communications, laser and computer technologies have all been achieved by altering the way light and other energy forms act naturally and how to manage them in a controlled manner. The results support the predicted ambipolar thermopower anisotropy in PdCoO 2.Throughout human history, the control of light, electricity and heat has evolved to become the cornerstone of various innovations and developments in electrical and electromagnetic technologies. ![]() The experimental data are consistently described by a combination of effective-medium models based on the main axes transport quantities. ![]() While the electronic transport of the polycrystalline samples is dominated by that of the Pd planes, the thermopower exhibits a well-defined deviation from the in-plane character at temperatures above 600 K, which is indicative of opposing trends in the Seebeck coefficients within and perpendicular to the delafossite layers. We report measurements of the high-temperature electrical resistivity, thermal conductivity, and thermopower of phase-pure PdCoO 2 powder compacts prepared by a highly Pd-efficient synthesis route. These properties are of interest for various applications, but have been difficult to verify because sufficiently large crystals have not been available. The layered delafossite PdCoO 2 has been predicted to be one of very few materials with a thermopower that is highly anisotropic and switches sign between different crystallographic directions.
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