Abstract
Superconductivity of 1 unit cell thick (1-UCT) YBa2Cu307 (YBCO) with various oxide cap layers is studied. Capping with BaO layer makes 1-UCT YBCO superconducting. It is revealed that that a formation of BaO-CuO-BaO charge reservoir is of significance for the hole donation in the 1-UCT YBCO. Superconductivity or significant reduction of resistivity implying the formation of the charge reservoir was also observed in 1-UCT YBCO covered with Sr-O, Ca-O, Pb-0, and Cd-O.
