Interlayer coupling effect in high-${\mathit{T}}_{\mathit{c}}$ superconductors probed by ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$/${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ superlattices

The effect of coupling between layers of the high-${\mathit{T}}_{\mathit{c}}$ superconductors was studied by varying both the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ and ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ layer thicknesses in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$/${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ superlattices. Superconductivity was found even when the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ layers had nominal thicknesses as small as 12 Å (one unit-cell thickness) but coupling between unit-cell layers is needed to achieve a ${\mathit{T}}_{\mathit{c}}$ of 90 K. The decrease of ${\mathit{T}}_{\mathit{c}}$ in isolated ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ layers with increasing sheet resistance is on the same scale of about ħ/${\mathit{e}}^2$ as observed for ordinary superconductors.