University of Birmingham > Talks@bham > Nanoscale Physics Seminars > Electron beams with a twist

Electron beams with a twist

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Twisted photons, or optical vortices, are special states of light containing orbital angular momentum, exemplified by the quanta of Laguerre-Gaussian and Bessel light beams. They have been studied extensively over the last two decades. One of the notable features of the optical vortices is that the transfer of orbital angular momentum from the vortex beam to the internal electronic systems of the atoms is forbidden in the dipole approximation. This has been predicted theoretically in 2002 [1] and has been confirmed experimentally [2, 3]. Twisted electrons, also called electron vortices, represent a very recent discovery. Predicted by Bliokh et al. [4], twisted electrons have been created inside electron microscopes in several laboratories [5-7]. Given the unusual result of the optical vortex with regarding to the transfer of orbital angular momentum, we have investigated the physics governing the orbital momentum transfer between the electron vortex beams and the atoms, both in terms of the centre of mass motion and in terms of ‘electronic transitions’. We will demonstrate that the coupling of the orbital angular momentum between the vortex beam and that of the center of mass motion of the atoms and that of the internal electronic dynamics are both allowed under the efficient dipole approximation [8]. This is contrary to the case of optical vortex. The implication for chiral electron energy-loss spectroscopy [6] as well as for possible nanoparticle manipulation will be explored. By comparing the cases for both types of vortex beams, we will also not only illustrate the different physics operating in the photon and electron cases respectively, but also the unique ways electron vortex may be explored but which are not available for the photon vortex beams. 0If time allows, initial experimental results in realizing electron vortex beams inside the electron microscopes in York will be presented.

[1] M Babiker, C Bennett, D Andrew and L Davila Romero, Phys. Rev. let. 89(14) (2002) 143601. [2] F Araoka, T Verbiest, K Clays and A Persoons, Phys. Rev. A71 (2005) 055401. [3] W Loffler, D Broer and J Woerdman, Phys. Rev. A83 (2011) 065801. [4] K Y Bliokh et al., Phys. Rev. Lett. 99 (2007) 190404 [5] M Uchida and A Tonomura, Nature 464 (2010), p. 737. [6] J Verbeeck et al, Nature 467 (2010), p. 301. [7] B J McMorran, et al. Science 331 (2011), p. 192. [8] S Lloyd, J Yuan and M Babiker, Phys. Rev. Lett. 108, (2012) 074802, S. Lloyd et al. (to be submitted)

This talk is part of the Nanoscale Physics Seminars series.

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