We summarize progress in the development and application of metamaterial structures utilizing superconducting elements. After a brief review of the salient features of superconductivity, the advantages of superconducting metamaterials over their normal metal counterparts are discussed. We then present the unique electromagnetic properties of superconductors and discuss their use in both proposed and demonstrated metamaterial structures.Finally we discuss novel applications enabled by superconducting metamaterials, and then mention a few possible directions for future research.Our objective is to give a basic introduction to the emerging field of superconducting metamaterials. The discussion will focus on the RF, microwave, and low-THz frequency range, because only there can the unique properties of superconductors be utilized. Superconductors have a number of electromagnetic properties not shared by normal metals, and these properties can be exploited to make nearly ideal and novel metamaterial structures. In section I. we begin with a brief overview of the properties of superconductors that are of relevance to this discussion. In section II we consider some of the shortcomings of normal metal based metamaterials, and discuss how superconducting versions can have dramatically superior properties. This section also covers some of the limitations and disadvantages of superconducting metamaterials. Section III reviews theoretical and experimental results on a number of unique metamaterials, and discusses their properties.Section IV reviews novel applications of superconducting metamaterials, while section V includes a summary and speculates about future directions for these metamaterials.
I. SuperconductivitySuperconductivity is characterized by three hallmark properties, these being zero DC resistance, a fully diamagnetic Meissner effect, and macroscopic quantum phenomena. 1 , 2 , 3 The zero DC resistance hallmark was first discovered by Kamerlingh Onnes in 1911, and has since led to many important applications of superconductors in power transmission and energy storage. The second hallmark is a spontaneous and essentially complete diamagnetic response developed by superconductors in the presence of a static magnetic field. As the material enters the superconducting state it will develop currents to exclude magnetic field from its interior. This phenomenon is known as the Meissner effect, and distinguishes superconductors from perfect conductors (which would not show a spontaneous Meissner effect).Finally, macroscopic quantum effects arise from the quantum mechanical nature of the superconducting correlated electron state.