Optically-induced effects in Y–ba–cu–O Josephson junctions

We report our studies on light-induced changes in electrical properties of YBa₂Cu₃O_x (YBCO) grain-boundary Josephson weak links. We discuss the erasable process (photodoping), in which light-induced enhancement of junctions properties at low temperatures relaxes back above 250 K. Our studies are focused on the junction critical current versus time, light intensity, and magnetic field measurements. In tested few-μm-wide step-edge junctions, photodoping manifested itself as above 50% increase of the critical current and the decrease of the junction magnetic penetration depth, leading to reduction of the effective junction width. Contrary to the photodoping effect, the high-intensity laser modification of junctions led to permanent modification of their electrical characteristics that remained unchanged after subsequent room-temperature/helium thermal cycling of the sample. The laser-modified junctions exhibited up to 25% increase of the critical current times normal-state resistance product.