Nonlocal response of Josephson tunnel junctions to a focused laser beam.

Abstract

The effect of a focused laser beam on the critical junction current of a one-dimensional Josephson tunnel junction is analyzed for both short and long junctions. The laser heating locally alters the critical current density and London penetration depth, giving rise to a change in the critical current which is proportional to the local current density of the irradiated region. In addition, the relative pair phase is modified in a nonlocal manner which gives rise to an additional contribution to the change in the critical current of the junction. For short junctions, this nonlocal phase modification contributes two parts to the junction critical current. One has the same spatial dependence as that of the current distribution itself, while the other is independent of the position of the laser beam. This latter contribution depends upon the applied magnetic field and is a signature of the nonlocal effect. For a long junction, the nonlocal phase contribution to the change in the junction critical current can give rise to dramatic effects when the applied magnetic field is less than a critical value ${H}_{c}$=\ensuremath{\Elzxh}c/(2ed${\ensuremath{\lambda}}_{J}$). In this case the spatial dependence of the laser-induced change in the critical current can be qualitatively different from the unperturbed current distribution.