Figure 1: Experimental geometry and electronic band structure measured by ARPES.

(a) Schematic drawing of the experimental geometry and a surface Brillouin zone of the Bi(111) surface are represented. The experimental geometry was preserved in the present study thanks to an electron deflector function of the photoelectron analyzer. The definition of the spin polarization direction is depicted in the image. The angle between the light and the analyzer was fixed to 50°. The surface normal corresponds to the analyzer axis. The green parallelogram represents the light incident plane that is along the mirror plane of the Bi(111) surface. For the p-(s-) polarization, the electric-field vector of the laser is parallel (perpendicular) to the light incident plane. The electric-field vector of the linearly polarized light can be continuously rotated: the θ represents the angle between the electric-field vector of the light and the mirror plane of the Bi(111) surface. (b) ARPES intensity image along the mirror plane on Bi(111). The ARPES data was recorded with the p-polarization. The spin-resolved data were measured at the wave numbers of k₁−k₄.