  Recent experiments have demonstrated that the superconducting critical
temperature may be improved in various metamaterial superconductor geometries.
Here, we present the results of a study of tin-based metamaterial
superconductors in the epsilon-near-zero (ENZ) and hyperbolic metamaterial
configurations. It was observed that Tc enhancement is significantly reduced
when the metamaterial structural dimensions exceed 240nm, the superconducting
coherence length in pure tin.
