Superconductivity in ultrathin films consisting of Bi2Sr2CaCu2O8+δ/Bi2Sr2CuO6+δ heterostructures

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Abstract
Superconductivity of a one‐primitive‐cell‐thick Bi2Sr2CaCu2O8+δ layer was investigated in ultrathin films consisting of Bi2Sr2CaCu2O8+δ/Bi2Sr2CuO6+δ heterostructures. Films were prepared directly on substrates of SrTiO3(001) with a molecular beam epitaxy technique. The number of CuO2 planes is fixed at six in all films, in which the one‐primitive‐cell‐thick Bi2Sr2CaCu2O8+δ layer is located at various positions with respect to the Bi2Sr2CuO6+δ layers, from the surface of films to the interface between films and substrates. We observed that the one‐primitive‐cell‐thick Bi2Sr2CaCu2O8+δ layer shows superconductivity when it is surrounded by Bi2Sr2CuO6+δ layers. Superconductivity of the Bi2Sr2CaCu2O8+δ layers is, however, destroyed if it is located at the surface or at the interface between films and substrates.