Correlation between the interlayer Josephson coupling strength and an enhanced superconducting transition temperature of multilayer cuprate superconductors

Abstract

Infrared reflectivity spectra of multilayered HgBa${}_{2}$Ca${}_{n\ensuremath{-}1}$Cu${}_{n}$O${}_{2n+2+\ensuremath{\delta}}$ ($n=2$, 3, 4, and 5) are measured. Optical plasma modes associated with the Josephson coupling between CuO${}_{2}$ planes within a multilayer appear below ${T}_{c}$ in the $c$-axis component of the reflectivity spectrum. The result allows for quantitative estimation of the interlayer Josephson coupling strength within a multilayer. It is found that the change of the Josephson coupling strength correlates with the increase of ${T}_{c}$ up to $n=3$ and the subsequent decrease for $n\ensuremath{\ge}4$.