Electronic properties of the Si(111)-7×7 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 ≥ 5 K vanishes by thermal fluctuations at T ≈ 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.

Electronic transport properties of the Si(111)-( √ 3 × √ 3)-Sn surface formed on low doped Si substrates are studied using two-probe conductivity measurements and tunnelling spectroscopy. We demonstrate that the ground state corresponds to Mott-Hubbard insulator with a band gap 2∆ = 70 meV, which vanishes quickly upon temperature increase. The temperature dependence of the surface conductivity above T > 50 K corresponds to the Efros-Shklovskii hopping conduction law. The energy gap at the Fermi level observed in tunnelling spectroscopy measurements at higher temperatures could be described in terms of dynamic Coulomb blockade approximation. The obtained localization length of electron is ξ = 7Å.

The Shapiro steps (ShSs) developing in sliding charge-density wave (CDW) under rf irradiation are considered in terms of the CDW travel in the periodic (washboard) potential. We demonstrate that treating the CDW as an inertialess object whose velocity is defined by the instantaneous voltage one can predict the positions of the ShSs in dc voltages for the given amplitude of rf voltage. Moreover, the approximation allows indicating the rf voltages at which the ShSs' magnitudes show maxima and minima. The only information necessary in advance is the I–V characteristic without rf irradiation and the cross-sectional area of the sample. Thus, one can recover the course of an I–V curve in average and the positions of ShSs on it, though not their forms.

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