  To realize a one-dimensional (1D) system with strong spin-orbit coupling is a
big challenge in modern physics, since the electrons in such a system are
predicted to exhibit exotic properties unexpected from the 2D or 3D
counterparts, while it was difficult to realize genuine physical properties
inherent to the 1D system. We demonstrate the first experimental result that
directly determines the purely 1D band structure by performing spin-resolved
angle-resolved photoemission spectroscopy of Bi islands on a silicon surface
that contains a metallic 1D edge structure with unexpectedly large Rashba-type
spin-orbit coupling suggestive of the nontopological nature. We have also found
a sizable out-of-plane spin polarization of the 1D edge state, consistent with
our first-principles band calculations. Our result provides a new platform to
realize exotic quantum phenomena at the 1D edge of the strong
spin-orbit-coupling systems.
