Generation of electron vortices using nonexact electric fields

Vortices in electron beams can manifest several types of topological phenomena, such as the formation of exotic structures or interactions with topologically structured electromagnetic fields. For instance, the wave function of an electron beam can acquire a phase vortex upon propagating through a magnetic monopole. In practice, this provides a convenient method for generating electron vortex beams, yet it is very limited by the structural integrity of devices used for such purposes. Here, we show how an electric field must be structured in order to achieve a similar effect. We find that closed but not exact electric fields can produce electron vortex beams. We proceed by fabricating a versatile, robust, and near-obstruction-free device that is designed to approximately produce such fields and we systematically study their influence on incoming electron beams. With such a single device, electron vortex beams that are defined by a wide range of topological charges can be produced by means of a slight variation of an applied voltage. For this reason, this device is expected to be important in applications that rely on the sequential generation and manipulation of different types of electron vortices.