Imaging flux vortices in type II superconductors with a commercial transmission electron microscope

Abstract

Flux vortices in superconductors can be imaged using transmission electron microscopy because the electron beam is deflected by the magnetic flux associated with the vortices. This technique has a better spatial and temporal resolution than many other imaging techniques and is sensitive to the magnetic flux density within each vortex, not simply the fields at the sample surface. Despite these advantages, only two groups have successfully employed the technique using specially adapted instruments. Here we demonstrate that vortices can be imaged with a modern, commercial transmission electron microscope operating at 300 kV equipped with a field emission gun, Lorentz lens and a liquid helium cooled sample holder. We introduce superconductivity for non-specialists and discuss techniques for simulating and optimising images of flux vortices. Sample preparation is discussed in detail as the main difficulty with the technique is the requirement for samples with very large (>10µm), flat areas so that the image is not dominated by diffraction contrast. We have imaged vortices in superconducting Bi 2 Sr 2 CaCu 2 O 8-δ and use correlation functions to investigate the ordered arrangements they adopt as a function of applied magnetic field.

Diamond magnetometry of superconducting thin films

“…[7]) and can serve as a model for condensed-matter flow [8]. Reduction of vortex motion has been achieved through the use and engineering of pinning centers [9,10]. * amirwaxm@bgu.ac.il…”

“…Magnetic imaging enables obtaining accurate values of the penetration depth, which reports on the number density of electrons involved in superconductivity, the nature of the superconducting state [11], and the types of vortex interactions which can occur [12]. Aside from capturing vortex structure, techniques that feature video frame rate may enable studies of vortex dynamics [10,13].…”

Imaging flux vortices in MgB2 using transmission electron microscopy

“…Antivortices are seen when the field goes negative as indicated by the reversal of the black-white contrast. To assess the ordering of the vortices, autocorrelation functions of the vortex positions, found by motif matching 9 , are shown to the right of each image. Histograms showing the distribution of vortex spacings and the angle which lines connecting neighbouring vortices ('bonds') make to the horizontal are shown in supp.…”

Magnetic structure of individual flux vortices in superconducting MgB2derived using transmission electron microscopy

“…As shown in ref. 10, much of the information on the structure of the vortex is contained in the contrast of the image rather than its visual appearance. Here we use images of flux vortices taken from MgB 2 to make a quantitative comparison with simulations to assess how much information can be obtained using transmission electron microscopy.…”