Anisotropic conductivity of the Si(111)4 × 1-In surface: Transport mechanism determined by the temperature dependence

The temperature dependence of anisotropic conductivity of a quasi-one-dimensional metallic surface, Si(111)4×1-In, was measured by a variable-temperature four-tip scanning tunneling microscope. Using the square four-point probe method, we succeeded in measuring the conductivity parallel and perpendicular to the In chains independently as a function of temperature. It was shown that the conductivity perpendicular to the In chains was mainly the conductivity of the space-charge layer of the substrate. Moreover, it was clarified that it strongly depends on the substrate flashing temperature and this sometimes hindered the anisotropic conductivity at low temperatures. In contrast, the conductivity parallel to In chains was clearly dominated by the surface states and decreased drastically around 110 K by the well-known 4×1 to 8×2 metal-insulator transition. The low temperature 8×2 phase had an energy gap as large as ∼250 meV, consistent with previous photoemission reports.