Lorentz microscopy observation of vortex dynamics due to transport current

Abstract

At present, Lorentz microscopy is the only one method to visualize individual vortices in superconductors and observe their motion in real time. Using this technique, we have investigated the fascinating vortex dynamics in superconductors, niobium and BSCCO. And recently we applied it to investigate current driven vortex motion.The vortices are driven by the Lorentz force due to the transport current, and begin to move. This couses the vortex to dissipate the energy i.e., causes the resistive state in the superconductor. Therefore to clarify the vortex motion is important especially in the relation with vortex pinning.The sample we examined was niobium thin film, which was single-crystallized by annealing and thinned by chemical etching. It was put in the low temperature specimen stage specially developed for the vortex observation, which was installed in 350 kV FE-TEM based Hitachi H-9000.We observed current driven vortex motion in the temperature (T) range from 4.5 K to Tc = 9.25 K and in a (externally applied) magnetic field (B) up to 100 Gauss.