Electron correlation effects in transport and tunneling spectroscopy of   the Si(111)-$7\times 7$ surface
  Electronic properties of the Si(111)-$7\times 7$ surface are studied using four- and two-probe conductivity measurements and tunneling spectroscopy. We demonstrate that the temperature dependence of the surface conductivity corresponds to the Efros-Shklovskii law at least in $10-100$~K temperature range. The energy gap at the Fermi level observed in tunneling spectroscopy measurements at $T\geq 5$~K vanishes by thermal fluctuations at $T\approx 30$~K, without any sign of the metal-insulator transition. We show that the low-temperature energy gap observed by the tunneling spectroscopy technique is actually the consequence of the Coulomb blockade effect. 
A.B. Odobescu, A.A. Maizlakh, and S.V. Zaitsev-Zotov
cond-mat.str-el cond-mat.mes-hall cond-mat.mtrl-sci