Nonmetallic Conduction in Electron Inversion Layers at Low Temperatures

We have measured the resistance of electron inversion layers in Si metal-oxide-semiconductor field-effect transistors at low temperatures (50 mK) and low electric fields (0. 1 V/m). At low values of R_ we observe logarithmic dependences of the resistance on both temperature and applied electric field which scale only on R_. We observe a gradual transition to an exponential dependence at R_10 k. The logarithmic dependences agree qualitatively but not quantitatively with current theories of localization.