Localization in a Nondegenerate Two-Dimensional Electron Gas

Magnetoresistance measurements of an electron gas formed on a solid-hydrogen substrate are reported as a function of surface disorder. High-mobility surfaces display an essentially classical positive B² field dependence. Lower-mobility surfaces, however, are characterized by the appearance of a negative magnetoresistance for fields less than {~}0.2 T, in good agreement with present weak-localization theories. On extremely disordered surfaces we find large increases in resistivity but a finite residual electron diffusivity D~mₑₗ.