Spin polarisation with electron Bessel beams

TL;DR

This paper explores the potential of using electron Bessel beams in electron microscopes as highly efficient spin polarizers, especially at low voltages, offering a new approach to spin filtering.

Contribution

It demonstrates that Bessel beams in standard magnetic lenses can be intrinsically spin polarized, with near 100% polarization achievable under ideal detection conditions.

Findings

Spin polarization approaches 100% with on-axis detectors.

Polarization drops below 10^-4 with standard detector sizes.

Low voltage operation significantly enhances spin filter performance.

Abstract

The theoretical possibility to use an electron microscope as a spin polarizer is studied. It turns out that a Bessel beam passing a standard magnetic objective lens is intrinsically spin polarized. In the limit of infinitely small detectors on axis, the spin polarisation tends to 100 % . Increasing the detector size, the polarisation decreases rapidly, dropping below 10^-4 for standard settings of medium voltage microscopes. For extremely low voltages, the figure of merit increases by two orders of magnitude, approaching that of existing Mott detectors. Our findings may lead to new desings of spin filters, an attractive option in view of its inherent combination with the electron microscope, especially at low voltage.