Title: Spin-split bands of Ag quantum film induced by
Rashba effect at a surface

Speaker: Prof. Iwao MATSUDA
Affiliation: Institute for Solid State Physics, the University of Tokyo

Date + Time: April 16th, 11:30-12:05
Place: UVSOR Build. #304 (UVSOR Seminar room)


Abstract
Spin controls in utrathin metal films have been important topics in developing
(nanometer-scale) spintronics and studying modern solid state physics. When
thickness of metal film reduces to electron wavelength, electron energy is
quantized by quantum size effect, resulting in formation of quantum-well states.
Spin-polarization of such a quantum film of Ag has been reported when the film
was grown on magnetic substrate (e.g. Fe). The spin-separation of confined
electronic bands originates from spin-polarized bulk bands of the ferromagnetic
metal substrate, which induces spin-dependent reflection phase shift at the
film/substrate interface. Here, we demonstrate much sophisticated way to realize
spin-split bands in a metal　(Ag) film on a semiconductor (Si) substrate. Instead
of utilizing whole substrate, we used a strong Rashba effect at a surface monatomic
layer. Due to the breakdown of inversion symmetry at a surface, spin degeneracy
of electrons can be lifted by spin-orbit coupling. Such spin-split bands have directly
been observed by angle-resolved photoemission spectroscopy (ARPES) for Au and
Bi crystal surfaces. Recently, electronic states of the √3×√ 3-Bi ordered phase
on Ag (111) surface were reported to show an unexpectedly large Rashba spin-splitting.
Since Ag (111) film on Si substrate is one of the best studied metal quantum-well system,
the film covered with the √3× √3-Bi/Ag surface is a perfect system to demonstrate
spin-splitting in Ag film by the surface Rashba effect. Through detailed ARPES experiments,
we measured breaks of spin-degeneracy of subbands of the QWS. The origin is likely
explained by band hybridization model in single electron regime, which indicates that
the QWSs can be spin-polarized by the spin-split surface states.