Electron holography of vortex lattices in superconductors

Abstract

The recent success in observing magnetic vortices in superconductors by means of transmission electron microscopy techniques has opened a new window to investigate the behavior of vortex lattices. We report the first direct observation of 2-D vortex lattices in niobium thin films taking advantage of the high resolution and sensitivity of electron holography.The experiments were conducted in a 300 keV field emission electron microscope equipped with a cold stage that allows magnetic fields to be applied while the specimen can be maintained from 30 K down to 4.5 K. The Nb specimen is tilted by 45° to the electron beam and the magnetic field is applied in the horizontal direction. The microscope also has a rotatable electron biprism used to form holograms. The thin (70±20 nm) foil specimens were prepared by chemically polishing 2 mm × 2 mm × 30 μm sections of Nb that had been annealed to ∼2000°C in a vacuum of 10-6 Pa.