简介: |
new kind of electron beam with spiral wavefronts, called electron vortex beam. Like typhoons, it has an ‘eye’ of zero transverse phase velocity at its axis. Quantum mechanically, such a beam carries well-defined orbital angular momentum. I will show how vortex beams can be produced at nanoscale and characterized. I will then discuss the interaction of such beams with atoms. Compared with optical vortex beams that have been studied intensively for more than a decade, electron vortex beams can transfer one unit of orbital angular momentum to the atom’s internal degree of motion following a dipole transition, opening ways for chiral-sensitive spectroscopy to be developed. Finally, I will demonstrate an ‘electron spanner effect’, the transfer of orbital angular momentum to the center of mass of the atoms, by showing reversible rotation of gold nanoparticles depending on the chirial charge of the vortex beam applied.
报告人介绍：
Prof. Yuan received his B.S degree from University of London in 1983 and Ph.D degree in University of Cambridge in 1988. From 1988 to 2011 he worked in University of Cambridge as a research associate and advanced research fellow. From 2001 to 2007 he was the Cheung Kong Professor of Materials Physics and Chemistry, Department of Materials Science and Engineering, Tsinghua University and from 2008 he has been the Professor of Nanophysics and Electron Microscopy, Department of Physics, University of York.
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