ORIGINS OF CONDUCTIVE LOSSES AT MICROWAVE-FREQUENCIES IN YBA2CU3O7-DELTA LAALO3/YBA2CU3O7-DELTA TRILAYERS DEPOSITED BY PULSED-LASER DEPOSITION/

Oriented YBa2Cu3O7-delta/LaAlO3/YBa2Cu3O7-delta trilayers were deposit ed by pulsed laser deposition (PLD) onto [100] MgO and LaAlO3. Film th icknesses varied from 2000-5000 Angstrom/layer. A comparision of struc ture and transport data for the bottom and top superconducting layers indicated a slight decrease in film quality for the top superconductin g layer. The critical temperature was lower for the top superconductin g layer (90.5 vs. similar to 90 K) and the microwave surface resistanc e was higher (increasing from similar to 2 to 18 m Omega at 36 GHz, 20 K). The resistivity of the dielectric was estimated to be 10(6) Omega cm, and the loss tangent of the dielectric film at microwave frequenc ies had an upper limit of 0.01. Cross-sectional TEM analysis of the tr ilayer structure showed a high density of threading dislocations in th e dielectric layer that appeared to nucleate at steps in the underlyin g superconducting layer. The threading dislocations may serve as condu ction paths in the LaAlO3 layer.