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 dc field induces only the second harmonic with a small value of slope ofV 2−H dc curve (δV 2/δH dc) compared to bulk YBCO. The variation of the amplitude of third harmonic (V 3) withH ac and temperature was studied. These results are explained in terms of a critical state model. The observation of only a small amplitude of second harmonic (V 2) with a smallδV 2/δH dc is explained in terms of a special kind of clean grain boundary present in YBCO laser ablated films on 〈100〉 MgO.