Proposal for an ultrafast spin-polarized nanotip photoemission electron source based on the spin Hall effect

We propose a new ultrafast laser-driven nanotip source of spin-polarized free electrons taking advantage of the spin Hall effect. A charge current is generated in a V-shaped conducting photocathode of nanometer size scale that supports the spin Hall effect at room temperature with a suitably large Hall angle and spin diffusion length [1]. The resultant induced transverse spin currents on the photocathode surfaces are thus expected to lead to electron spins of opposing signs on opposite walls, and a fraction of the polarized electrons beneath the photoemitting convex surface at the tip of the V would be transversely polarized. The polarization direction of the output beam could be flipped simply by switching the polarity of the voltage source driving the current through the V-shaped photocathode. Search for optimal fabrication processes is underway. It is possible that such photocathodes could be fabricated from commercially-available tungsten V-shaped AFM cantilevers.

[1] K. M. Bastiaans, M.Sc. Thesis, Leiden University (2015).