Position, spin, and orbital angular momentum of a relativistic electron

KY Bliokh, Mark Dennis, Franco Nori

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)
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Motivated by recent interest in relativistic electron vortex states, we revisit the spin and orbital angular momentum properties of Dirac electrons. These are uniquely determined by the choice of the position operator for a relativistic electron. We consider two main approaches discussed in the literature: (i) the projection of operators onto the positive-energy subspace, which removes the Zitterbewegung effects and correctly describes spin-orbit interaction effects, and (ii) the use of Newton-Wigner-Foldy-Wouthuysen operators based on the inverse Foldy-Wouthuysen transformation. We argue that the first approach [previously described in application to Dirac vortex beams in K. Y. Bliokh et al., Phys. Rev. Lett. 107, 174802 (2011)] has a more natural physical interpretation, including spin-orbit interactions and a nonsingular zero-mass limit, than the second one [S. M. Barnett, Phys. Rev. Lett. 118, 114802 (2017)].
Original languageEnglish
Article number023622
Number of pages9
JournalPhysical Review A: Atomic, Molecular and Optical Physics
Publication statusPublished - 28 Aug 2017


  • Angular momentum of light
  • Relativistic wave equations
  • Spin-orbit coupling

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