Laser-induced modification of transport properties of Y–Ba–Cu–O step-edge weak links

We report on the laser-induced permanent changes of the critical current (Ic) and normal resistance (Rn) of YBa2Cu3O72x ~YBCO! step-edge Josephson junctions. The 2to 20-mm-wide junctions were prepared from a 200-nm-thick YBCO film deposited by a pulsed KrF excimer laser onto 300-nm-high steps etched in the LaAlO3 substrate. The laser modification experiments were performed by illuminating the junctions at 50 K with a focused Ar-ion laser beam of various intensities. Depending on the illumination power density, either increase or decrease of the junction Ic has been observed. In particular, after illumination at the 0.6310 5 W/cm power level, a 75% enhancement of Ic and increase of the IcRn product up to 25% were obtained without a measurable change in the junction critical temperature. The laser-induced modifications were very reproducible and remained unchanged even after a subsequent room-temperature/helium thermal cycling of the sample. Photoassisted, thermally activated oxygen redistribution in the YBCO grain boundary region is proposed to explain the observed behavior. © 1995 American Institute of Physics.