Surface-State Electrical Conductivity at a Metal-Insulator Transition On Silicon

A quasi-one-dimensional metallic Si(111)-(4×1)-In surface was investigated by a newly developed temperature-variable microscopic four-point probe method combined with in situ electron diffraction in ultrahigh vacuum. We have succeeded, for the first time, in detecting directly a surface metal-insulator transition around 130 K as a dramatic change of electrical conductivity through the surface states. An energy gap of ~300 meV at the low-temperature phase, influences of defects and phase locking between the neighboring charge-density-wave chains were elucidated from the temperature dependence of conductivity.