Physical Review Letters 2017-07-18

Nonuniform Currents and Spins of Relativistic Electron Vortices in a Magnetic Field

Koen van Kruining, Armen G. Hayrapetyan, and Jörg B. Götte

Index: 10.1103/PhysRevLett.119.030401

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Abstract

We present a relativistic description of electron vortex beams in a homogeneous magnetic field. Including spin from the beginning reveals that spin-polarized electron vortex beams have a complicated azimuthal current structure, containing small rings of counterrotating current between rings of stronger corotating current. Contrary to many other problems in relativistic quantum mechanics, there exists a set of vortex beams with exactly zero spin-orbit mixing in the highly relativistic and nonparaxial regime. The well-defined phase structure of these beams is analogous to simpler scalar vortex beams, owing to the protection by the Zeeman effect. For states that do show spin-orbit mixing, the spin polarization across the beam is nonuniform rendering the spin and orbital degrees of freedom inherently inseparable.