Metal-Insulator Transition on the Ge(001) Surface

High-resolution angle-resolved photoemission studies of the Ge(001) surface are reported which clearly indicate the existence of a metallic surface state whose emission is observed over a narrow range of parallel momenta near the center of the surface Brillouin zone. The state slowly disappears as the temperature is lowered from room temperature to 77 K. This metal-insulator transition is coincident with a recently predicted and observed transition from a disordered to an ordered $c(4\mathrm{}\times 2)$ structure.