HIGH CRITICAL CURRENT DENSITIES IN ULTRATHIN YBA2CU3O7-DELTA FILMS SANDWICHED BETWEEN (PRXY1-X)BA2CU3O7-DELTA LAYERS

YBa2Cu3O7-delta (YBCO) films with nominal thicknesses of 1-4 unit cells were grown by pulsed laser deposition using (PrxY1-x)Ba2Cu3O7-delta [(PrY1-x)BCO] (1 greater-than-or-equal-to x greater-than-or-equal-to 0) as buffer layers and cap layers. The films of 1 unit cell thick were superconducting for all the x values while T(c) increased when x was reduced. For adjacent layers of (Pro.6Y0.4)BCO which is semiconducting, a T(c) of 43 K and J(c) of 2 X 10(6) A/cm2 for B parallel-to ab and 4 X 10(5) A/cm2 for B perpendicular-to ab at B = 7 T and 4.2 K were obtained in a one-unit cell thick YBCO layer. The J(c) values of a few unit cell thick YBCO layers nearly approached that of thick YBCO films. The results suggest the absence of significant weak-link effects in these films.