Synthesis of Bi2Sr2CaCu2O8/Bi2Sr2CuO6 superlattices with a Tc enhancement effect.

${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$(2212)/${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CuO}}_{6}$(2201) superlattices epitaxially grown in situ by reactive rf magnetron sputtering on heated MgO substrates were studied by x-ray diffraction methods and resistive measurements. The highest ${\mathit{T}}_{\mathit{c}}$(R=0) of 94 K, notably higher than that of single phase 2212 films prepared in the same conditions (${\mathit{T}}_{\mathit{c}}$=75--80 K), was obtained for (2212${)}_{\mathit{m}}$/(2201${)}_{\mathit{n}}$ superlattices where the number m of c-axis half-unit cells are close to unity. We attribute this fact to the metallic nature of the intervening 2201 layer favoring in such a situation an optimal ${\mathrm{O}}_{2}$ doping of the 2212 layers.