Surface Intervalley Scattering on GaAs(110): Direct Observation with Picosecond Laser Photoemission

Angle-resolved laser photoemission investigations of the laser-excited GaAs(110) surface have revealed a previously unobserved valley of the $C_3$ unoccupied surface band whose minimum is at $\overline{X}$ in the surface Brillouin zone. Electron population in this valley increases only as a result of scattering from the directly photoexcited valley at $\overline{\Gamma }$. With high momentum resolution, we have isolated the dynamic electron population changes at both $\overline{\Gamma }$ and $\overline{X}$ and deduced the scattering time between the two valleys.