Beam Physics Seminar
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