Growth and superconductivity of single one unit‐cell YBa2Cu3O7−x Layer

Structure and superconductivity of ultrathin films as thin as a unit‐cell size have been investigated. Oscillations in the reflection high energy electron diffraction (RHEED) specular intensity during growth of the superconducting oxides on SrTiO3 indicate that the growth occurs in monomolecular layer by monomolecular layer mode. The film thickness can be exactly controlled by monitoring the RHEED intensity. The isolated ultrathin YBa2Cu3O7−x (YBCO) films sandwiched in between PrBa2Cu3O7−x (PrBCO) layers were prepared using the growth interruption technique by oscillations monitoring. A one unit‐cell YBCO layer has a superconducting transition with the onset temperature at 70K and the zero resistance at 30K. The overlayer of PrBCO was required to provide the underlying one unit‐cell YBCO layer with hole carriers sufficient to induce superconductivity. The reduction of the onset temperature is found to be mainly due to the decrease of the hole carriers but not due to the absence of the interlayer coupling....