Application of metamaterial nano-engineering for increasing the superconducting critical temperature*

In previous work, we demonstrated that the metamaterial approach to dielectric response engineering increases the critical temperature of a composite superconductor-dielectric system in the epsilon near zero (ENZ) and hyperbolic regimes. To create such metamaterial superconductors three approaches were implemented: 1) mixtures of tin and barium titanate nanoparticles of varying composition and tin and strontium titanate nanoparticles, 2) composite Al₂O₃-coated aluminium nanoparticles, and 3) thin Al/Al₂O₃heterostructures that form a hyperbolic metamaterial superconductor. IR reflectivity measurements confirmed the predicted metamaterial modification of the dielectric function thus demonstrating the efficacy of the metamaterial approach to T_c engineering. In this talk, we present specific heat data on samples of the composite Al₂O₃-coated aluminium nanoparticles showing that the normal state density of states (DOS) is similar to that of pure aluminum, thus precluding the DOS from being responsible for the observed enahanced T_c. We will also discuss other features in the specific heat results that are consistent with results of neutron scattering experiments.