Microscopic Imaging of Josephson Junction Dynamics

Abstract

Josephson junctions show various dynamical regimes including cavity waves and nonlinear solitonic excitations. The use of spatially resolved measurements is important to further our knowledge about the junction dynamics. We present experimental results obtained by low-temperature scanning electron microscopy offering a spatial resolution of about 1 μm. This technique offers the possibility to probe the dynamics in the time average by applying a weak and localized thermal perturbation. With the appropriate electron beam power this perturbation does not destroy the dynamical state of the junction. A theoretical approach relating the obtained images to real junction dynamics is presented. We show examples of our imaging results dealing with cavity modes, single-, and multi-soliton dynamics in Josephson tunnel junctions made from Nb and Pb-alloy superconductors as well as cavity modes in grain boundary Josephson junctions made from the high-critical-temperature superconductor YBa2Cu3O 7-δ. With high-quality Nb and Pb-alloy junctions we are able to confirm existing theoretical models about cavity resonances and soliton dynamics. Furthermore, we prove the existence of soliton-type motion along the diagonals of square junctions predicted theoretically, discover several stable multi-soliton modes, and directly show the Lorentz contraction of solitons.