EFFECT OF LIGHT IRRADIATION ON FISKE RESONANCES AND THE JOSEPHSON EFFECT IN HIGH-T-C JUNCTIONS

We have performed photoexcitation experiments in high T-c YBa2Cu3Ox gr ain-boundary Josephson junctions. While the Josephson critical current is substantially enhanced, the normal state resistance decreases, and the positions of the extreme in the Fraunhofer diffraction pattern re main unchanged. These measurements show that the magnetic field penetr ation depth is not affected by light irradiation. On the other hand, t he position and intensity of Fiske steps due to electromagnetic resona nces increase substantially, which implies that the ratio of the thick ness barrier to the dielectric constant changes by a factor of 2.