EFFECT OF PHOTODOPING ON THE FISKE RESONANCES OF YBA2CU3OX GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS

We have expanded our studies on illuminated YBa2Cu3Ox, grain boundary Josephson junctions (GBJJ) which show both de Josephson properties (Fr aunhofer pattern) and ac Josephson properties (Fiske resonance). Illum inating GBJJs with visible light changes the Josephson coupling. This change is characterized by an increase of the critical current and a l arge shift in the voltage position of the Fiske resonances. This effec t is due to persistent photoinduced superconductivity (PPS) of the oxy gen-depleted YBa2Cu3Ox, barrier, similar to the PPS found in illuminat ed oxygen-deficient YBa2Cu3Ox, thin films. From Fiske resonance experi ments in GBJJs of different lengths, it is possible to study the veloc ity of the electromagnetic wave in the barrier and its change after il lumination. Information on the parameters of the barrier, before and a fter illumination, is obtained from this study.