A Novel Approach to Production of Highly Spin Polarized Electrons from III-V Semiconductor/Half-Metal Hybrid Multilayers

GaAs system are an important source of spin polarized electrons which are used in accelerator experiments to unravel the mystery of the elementary particles, origin of proton spin and domain dynamics in magnetic and ferroelectric systems. Although the theoretical limit in GaAs photocathodes is 50 % but only 35 % is routinely achieved in experiments. The growth of strained superlattice push up the production cost of the photocathodes. We will grow ultrathin epitaxial half-metal Heusler alloys as spin filters on GaAs photocathodes. Half-metals have 100 % spin ordering. The growth of an epitaxial spin filter with 100% spin alignment for selective spin filter allowing emission of electron of a particular spin orientation will increase the polarization yield beyond the theoretical limit. These half metal Heusler alloy/GaAs devices are expected to have polarization yields comparable to the strained GaAs superlattice systems. In Phase I we plan to put efforts in the following two research directions. First we will develop an advanced predictive algorithm based on DFT calculations to select the best lattice matched half- metal/GaAs system. The optimized systems will be fabricated using advanced MBE techniques for defect free epitaxial interface. P and QE tests will be carried out in the final stages to characterize the hybrid photocathodes. Spin-polarized electron sources are uniquely suited to applications in nuclear and particle physics. In order to learn the mystery of the “missing” proton spin, the US National Academy of Sciences in 2018 gave its backing to a new machine, the electron-ion collider EIC), in which an intense spin-polarized electron beam collides with intense beams of both polarized nucleons and unpolarized nuclei to reveal their inner secrets.