Recent experiments have shown the viability of the metamaterial approach to dielectric response engineering for enhancing the transition temperature, Tc, of a superconductor. In this report, we demonstrate the use of Al2O3-coated aluminium nanoparticles to form the recently proposed epsilon near zero (ENZ) core-shell metamaterial superconductor with a Tc that is three times that of pure aluminium. IR reflectivity measurements confirm the predicted metamaterial modification of the dielectric function thus demonstrating the efficacy of the ENZ metamaterial approach to Tc engineering. The developed technology enables efficient nanofabrication of bulk aluminium-based metamaterial superconductors. These results open up numerous new possibilities of considerable Tc increase in other simple superconductors.

Transformation optics gives rise to numerous unusual optical devices, such as novel metamaterial lenses and invisibility cloaks. Very recently, Mattheakis et al. (Luneburg lens waveguide networks. J. Opt. 2012, 14, 114006) have suggested theoretical design of an optical waveguide, based on a network of Luneburg lenses, which may be useful in sensing and nonlinear optics applications. Here, we report the first experimental realization of such Luneburg waveguides. We have studied wavelength and polarization dependent performance of the waveguides.

Recent experiments have shown the viability of the metamaterial approach to dielectric response engineering for moderately enhancing the transition temperature, Tc, of a superconductor. In this report, we demonstrate the use of Al2O3-coated aluminium nanoparticles to form the recently proposed epsilon near zero (ENZ) core-shell metamaterial superconductor with a Tc that is three times that of pure aluminium. IR reflectivity measurements confirm the predicted metamaterial modification of the dielectric function thus demonstrating the efficacy of the ENZ metamaterial approach to Tc engineering. These results provide an explanation for the long known, but not understood, enhancement of the Tc of granular aluminum films.

A dielectric response function plays a significant role in electron-electron interaction. Recently we proposed that the metamaterial approach to dielectric response engineering may increase the superconducting critical temperature. A composite superconductor-dielectric metamaterial has been tested in experiments with compressed mixtures of tin and barium titanate nanoparticles of varying composition. An increase of the critical temperature of the order of 5 percent compared to bulk tin has been ob-served [1]. Measurements of dielectric function was found to be in agreement with our model. A role of dielectric and particle size will be demonstrated. Different metamaterial approaches will be discussed [2]. [1]. V. N. Smolyaninova, et al., Sci-entific Reports 4, 7321 (2014); [2]. I. Smolyaninov and V. N. Smolyaninova, Phys. Rev. B 91, 094501 (2015)