Poster Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

Electron holography of high temperature superconductors – experiences and learnings (#263)

Anne-Helene Puichaud 1 , Ruth Knibbe 1 , Sadegh Yazdi 2 , Takeshi Kasama 2 , Stuart Wimbush 1 , Nick Strickland 1 , Evgeny Talantsev 1
  1. Victoria University of Wellington, Lower Hutt, NEW ZEALAND, New Zealand
  2. Center for Electron Nanoscopy, Technical University of Denmark, Lyngby, Denmark

Medium resolution electron holography is a transmission electron microscopy (TEM) technique which can be used to study magnetic and electric fields.  This technique has been used by researchers to study magnetic vortex formation and migration in type-II superconductors with mixed success. The understanding of magnetic vortex migration and the pinning of vortices by microstructural defects is important as it is the principal mechanism which defines the superconductor wire's current-carrying capacity1.

Two electron holography techniques can be used to study the magnetic vortices: off-axis or in-line electron holography. Quantitative information about magnetic and electric fields can be obtained from the off-axis technique, whereas with in-line electron holography, also called coherent beam Lorentz microscopy, vortex migration can be observed. Previous work has been done by Tonomura and co-workers on YBa2Cu3O7-δ (YBCO) single crystals2  using the 1 MeV transmission electron microscope they developed3.

In this current project, we are attempting to use in-line and off-axis electron holography, with a 300 keV probe-corrected FEI Titan, to study magnetic vortices in both YBCO crystals and for the first time in practical polycrystalline YBCO wire. Many challenges have been encountered including sample inhomogeneity, geometry and preparation. In particular, the observation of magnetic vortices in-situ requires that the sample be cooled with liquid helium, presenting further experimental restraints. In this presentation, I will discuss the experiences and learnings we have with electron holography of YBCO over the past year. 

  1. Obradors. X et al., Growth, nanostructure and vortex pinning in superconducting YBa2Cu3O7 thin-films based on trifluoroacetate solutions”, Supercond. Sci. Technol, Vol 25, Art. No. 123001 (2012).
  2. Tonomura. A, et al., Observation of Structure Chain Vortices Inside Anisotropic High-Tc Superconductors”, Phys. Rev. Lett, Vol 88, No 237001 (2002)
  3. Kawasaki. T et al., “Fine crystal lattice fringes observed using a transmission electron microscope with 1 MeV coherent electron waves”, Applied Physics Letters, Vol 76, No 1342 (2000)