Spin-orbit interaction (SOI) in low-dimensional systems, namely Rashba
systems and the edge states of topological materials, is extensively studied in
this decade as a promising source to realize various fascinating spintronic
phenomena, such as the source of the spin current and spin-mediated energy
conversion. Here, we show the odd fluctuation in the spin-orbital texture in a
surface Rashba system on Bi/InAs(110)-(2×1) by spin- and angle-resolved
photoelectron spectroscopy and a numerical simulation based on a
density-functional theory (DFT) calculation. The surface state shows a paired
parabolic dispersion with the spin degeneracy lifted by the Rashba effect.
Although its spin polarization should be fixed in a particular direction based
on the Rashba model, the observed spin polarization varies greatly and even
reverses its sign depending on the wavenumber. DFT calculations also reveal
that the spin directions of two inequivalent Bi chains on the surface change
from nearly parallel (canted-parallel) to anti-parallel in real space in the
corresponding wavevector region. These results point out an oversimplification
of the nature of spin in Rashba and Dirac systems and provide more freedom than
expected for spin manipulation of photoelectrons.Comment: 23 pages, 7 figure