Real-Time Observation of the Interaction between Flux Lines and Defects in a Superconductor by Lorentz Microscopy

Abstract
Flux lines in a Nb thin film at 4.5 K were observed by using a 300-kV field-emission transmission electron microscope equipped with a TV system. When the magnetic field applied to the film was suddenly changed, flux lines moved until arriving at an equilibrium state by hopping from one pinning center to another. Frame-by-frame observation of videotape recorded with a time resolution of 1/30 s revealed how individual flux lines behaved when they came across subgrain boundaries, and interacted with the boundaries.