Electrons with Topological Charge
Peter Schattschneider 1, 2
1 Institute of Solid State Physics, Vienna University of Technology, Karlsplatz, Vienna, Austria 2 Ecole Centrale Paris,UMR8579, Châtenay-Malabry, France
17:15 - 18:15 Tuesday 23 April 2013 TUG P2 Electron vortex beams are free electrons with topological charge, characterized by a spiraling wavefront and a phase singularity at the center, similar to optical vortices that were theoretically described by Nye and Berry 40 years ago. According to their quantized angular momentum they carry a magnetic moment m, contrary to optical vortices.
Nanometer sized electron vortex beams can now be produced in the electron microscope using computer generated holograms or astigmatic lenses. This technique opens an avenue for the practical use of electron vortex beams. For instance, transfer of angular momentum from vortices is used in Energy Loss Magnetic Chiral Dichroism (EMCD), the electron equivalent of XMCD (X-ray Magnetic Circular Dichroism), giving atom-specific magnetic moments in ferromagnetic materials.
Other innovative applications can be envisaged since the magnetic moment associated with an electron vortex of topological charge m couples to the magnetic field of spin polarized target atoms. Vortices could thus serve as electron tweezers to trap and move single atoms and molecules.
An overview is given over the current understanding and application of vortex electrons, stressing recent results such as their peculiar rotation behaviour in magnetic fields, nanometric resolution in EMCD, and spin maps of individual atomic columns.
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