Nonlocal response of grain-boundary-type Josephson junctions to local perturbation

The effect of a focused electron or laser beam on the critical current of Josephson junctions with grain-boundary geometry is analyzed using a numerical iteration method. Beyond a change in the critical current which is proportional to the local critical current density in the irradiated junction region, there is an additional change of the critical current due to a nonlocal modification of the phase difference function. For Josephson junctions larger than the Josephson penetration depth this nonlocal contribution is significant and the total electron beam induced change of the critical current is no longer proportional to the local Josephson current density. Our model calculations are compared to experimental results obtained from the analysis of YBa2Cu3O7-δ grain-boundary Josephson junctions (GBJ's) using low temperature scanning electron microscopy (LTSEM). Comparing the LTSEM measurements to the model calculations gives information on the spatial homogeneity of the critical current density, the influence of the junction geometry on the distribution of the Josephson current density, and the spatial structure of static magnetic flux states