Electron Microscopy Study on Magnetic Flux Lines in Superconductors: Memorial to Akira Tonomura

Using electron holography and coherent beam Lorentz microscopy, Akira Tonomura investigated the physics of magnetic flux lines, or vortices, in metal and high-temperature superconductors for more than 20 years. The methodology he developed for doing this made use of coherent electron waves from cold-emission (field-emission) sources and their quantum-mechanical phase shifts. Using 300-kV and 1-MV electron microscopes, Tonomura and his team clarified the dynamic behavior of magnetic flux lines in Pb and Nb superconductors and in high-temperature YBa
₂
Cu
₃
O
_7-δ
and Bi
₂
Sr
₂
CaCu
₂
O
_{8 + δ}
superconductors. This memorial paper reviews the static and dynamic flux-line behaviors in superconductors as revealed by their results.