SUPERCONDUCTING PROPERTIES OF DOPED-YBCO ULTRA-THIN FILMS

We report the properties of doped YBa2Cu3O7-gamma, (YBCO) ultra thin f ilms on SrTiO3 (100) substrates as a function of film thickness and do pant concentration. 20 nm-thick ultra thin films of Y0.7Ca0.3Ba2Cu3O7- gamma (Ca-YBCO), Y1-xPrxBa2Cu3O7-gamma (x Pr-YBCO, x = 0.1, 0.3, and 0 .5), and YBa2Cu2.79Co0.21O7-gamma (Co-YBCO) were deposited by pulsed l aser deposition. We measured the zero resistance temperature (T-c,T-0) of 55, 67, and 35 K for Ca-YBCO, 0.1 Pr-YBCO, and 0.3 Pr-YBCO films, respectively. PrBa2Cu3O7-x(PBCO) buffer layer was essential to obtain the superconducting Co-YBCO films with T-c,T-0 of 53 K. This is explai ned in terms of lattice distortion owing to grabing extra oxygen by su bstituting Co for Cu site in the Cu-O chain layer and stress relaxatio n of the film by inserting the PBCO buffer layer.