HARMONIC-GENERATION STUDIES IN LASER-ABLATED YBCO THIN-FILM GROWN ON [100] MGO

The generation of harmonics in a laser ablated YBCO film deposited on a [100] MgO substrate is reported. Higher odd harmonics appeared when the film was subjected to an ac field. The presence of a de field indu ces only the second harmonic with a small value of slope of V-2-H-dc c urve (delta V-2/delta H-dc) compared to bulk YBCO. The variation of th e amplitude of third harmonic (V-3) with H-ac and temperature was stud ied. These results are explained in terms of a critical state model. T he observation of only a small amplitude of second harmonic (V/(2)) wi th a small delta V-2/delta H-dc is explained in terms of a special kin d of clean grain boundary present in YBCO laser ablated films on [100] MgO.