title: Origins and demonstrations of electrons with orbital angular momentum.
abstract: The surprising message of Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)) was that photons could possess orbital angular momentum in free space, which subsequently launched advancements in optical manipulation, microscopy, quantum optics, communications, many more fields. It has recently been shown that this result also applies to quantum mechanical wave functions describing massive particles (matter waves). This article discusses how electron wave functions can be imprinted with quantized phase vortices in analogous ways to twisted light, demonstrating that charged particles with non-zero rest mass can possess orbital angular momentum in free space. With Allen et al. as a bridge, connections are made between this recent work in electron vortex wave functions and much earlier works, extending a 175 year old tradition in matter wave vortices.This article is part of the themed issue 'Optical orbital angular momentum'.
authors.affiliation: Department of Physics, University of Oregon, Eugene, OR, USA mcmorran@uoregon.edu.
authors.forename: Benjamin J
authors.identifier: http://orcid.org/0000-0001-7207-1076
authors.initials: BJ
authors.lastname: McMorran
authors.affiliation: Center for Nanoscale Science and Technology, National Institute of Standards Technology, Gaithersburg, MD 20899, USA.|Maryland NanoCenter, University of Maryland, College Park, MD 20742, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Agrawal
authors.affiliation: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Ercius
authors.affiliation: Department of Physics, University of Oregon, Eugene, OR, USA.|CNR-Istituto Nanoscienze, Centro S3, Via G. Campi 213/a, 41125 Modena, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Grillo
authors.affiliation: Materials Measurement Laboratory, National Institute of Standards Technology, Gaithersburg, MD 20899, USA.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Herzing
authors.affiliation: Department of Physics, University of Oregon, Eugene, OR, USA.
authors.forename: Tyler R
authors.initials: TR
authors.lastname: Harvey
authors.affiliation: Corrected Electron Optical Systems GmbH, Englerstraße 28, 69126 Heidelberg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Linck
authors.affiliation: Department of Physics, University of Oregon, Eugene, OR, USA.
authors.forename: Jordan S
authors.initials: JS
authors.lastname: Pierce
keywords: electron vortex; matter wave interferometry; optical angular momentum