Beam Physics Seminar

Friday, March 14, 2003, 10:00 AM
ARC Bldg. Room 231/233

Design of a new material for high-efficiency spin-polarized electron source

Anderson Janotti
Oak Ridge National Laboratory

High-quality spin-polarized electron source (SPES) is of fundamental importance in the investigation of spin-dependent phenomena in atomic, condensed-matter, and high-energy physics. Currently, almost all sources in use with accelerators are based on photoemission from GaAs and related materials.1 Although GaAs is an efficient photoemitter, the maximum polarization of the emitted electrons is limited to 50%, due to the degeneracy at the valence band maximum.2 Generally speaking, an ideal material for SPES application should have both large spin-orbit and positive crystal-field splitting. For this reason, strained GaAs grown on GaAsP3 or InGaAs4 grown on GaAs have been utilized. Nevertheless, the reduced critical layer thickness of these strained films leads to poor material quality and, consequently, low quantum efficiency. Tetragonal chalcopyrite ternary compounds have also been considered. However, since all these compounds have zero or negative crystal field splitting, the achieved polarization and quantum efficiency are rather low. In this talk we will address the proposal of a new material for high-quality SPES: AgGaSe2 in the CuAu phase. We show that with appropriate choice of the substrate, it is possible to grow epitaxially strain-free AgGaSe2 in the CuAu phase. Since this material has a direct-band gap, a large spin-orbit splitting, as well as a large positive crystal-field splitting, it is predicted to be a promising material for SPES with a 100% spin polarization.

Talk Slides: PDF