Application of metamaterial engineering to ultrathin TiN films: insulator to superconductor*

It is well known that decreasing the film thickness of superconducting thin films commonly leads to a decrease of the superconducting critical temperature, T_c. Ultrathin TiN films are insulating for the film thickness of 4.5 nm and below.  However, using ultrathin TiN layers with thickness below 4.5 nm in hyperbolic metamaterial TiN/dielectric multilayers restores superconductivity.  The electronic transport and anisotropy of optical properties of TiN/dielectric multilayers were studied. Enhancement of the T_c and the critical field in these metamaterials was found. The role of dielectric material and variation of thicknesses of superconductor and dielectric will be discussed.