SUPERCONDUCTING PROPERTIES OF ULTRATHIN Y(DY)BA2CU3O7 LAYERS IN Y(DY)BA2CU3O7-PRBA2CU3O7 HETEROSTRUCTURES

We have measured the superconducting properties of ultra thin layers o f YBa2Cu3O7 in C-axis YBa2Cu3O7-PrBa2Cu3O7 (YBCO-PrBCO) heterostructur es. These structures contain one or a few layers of YBCO (or in some c ases DyBCO). The critical temperature of single layers was investigate d through a series of PrBCO-YBCO-PrBCO trilayers. The trilayers consis t of d angstrom of YBCO sandwiched between a buffer and a capping PrBC O layer. The YBCO thicknesses were not chosen to be multiples of a uni t cell (approximately 12angstrom), but equal to n1/3 of a unit cell. The series was built with nominal YBCO thicknesses of approximately 4a ngstrom, approximately 8angstrom, approximately 12angstrom, double lin e arrow pointing right approximately 4angstrom. Superconductivity is o bserved in all the samples, except in the 4angstrom one which displays a pronounced semiconducting behavior. We discuss these results and th e differences between the properties of single and multilayer structur es.