SPATIALLY-RESOLVED STUDY OF THE DYNAMICS OF JOSEPHSON TUNNEL-JUNCTIONS

By scanning superconducting Nb/Al2O3/Nb tunnel junctions of various ge ometries with an electron beam at low temperatures we have obtained sp atially resolved two-dimensional images related with the dynamics of t he junctions. In a current-biased junction the local thermal perturbat ion effected by the beam results in a voltage change DELTAV representi ng a convenient imaging-response signal. The spatial resolution is lim ited by a characteristic thermal healing length with a value of about 2 mum in our experiments. We analyze our results in terms of the sine- Gordon equation. For the interpretation of the spatially resolved volt age signal DELTAV we extend the energetic analysis of the perturbed si ne-Gordon system of McLaughlin and Scott by including the beam-induced local thermal perturbation. Our model allows the quantitative compari son of our experimental two-dimensional images with the local dynamics expected from the perturbed sine-Gordon equation. Our experiments inc lude the observation of single-mode and multiple-mode cavity resonance s, soliton oscillations, and flux-flow behavior.