3RD-ORDER NONLINEAR MICROWAVE RESPONSE OF YBA2CU3O7-DELTA THIN-FILMS AND SINGLE-CRYSTALS

The nonlinear microwave response of superconducting YBa2Cu3O7-delta th in films and crystals was studied quantitatively by measuring the thir d-order harmonic amplitude E-3 omega (omega: 35 GHz, j(RF)less than or equal to 3 X 10(4) A/cm(2)). We find E-3 omega to be dominated by two extrinsic effects: (1) the interaction with flux lines in weak links, leading to an increased nonlinear response at low temperatures, and ( 2) rf related flux line creation at film edges, yielding a high E-3 om ega-signal close to T-c. Both effects together lead to a minimum in E- 3 omega around 40-60 K, which makes this temperature interval interest ing for rf applications. Intrinsic nonlinearities are smaller by order s of magnitude and could not be detected. (C) 1997 American Institute of Physics.