Linear temperature dependence of the conductivity in Si two-dimensional electrons near the apparent metal-to-insulator transition

In a high mobility two-dimensional electron system in Si, near the critical density, nc =0.32× 1011 cm-2, of the apparent metal-to-insulator transition, the conductivity displays a linear temperature (T) dependence around the Fermi temperature. When σ0, the extrapolated T=0 conductivity from the linear T dependence, is plotted as a function of density, two regimes with different σ0 (n) relations are seen, suggestive of two different phases. Interestingly, a sharp transition between these two regimes coincides with nc, and σ0 of the transition is ∼ e2 /h, the quantum conductance, per square. Toward T=0, the data deviate from linear σ(T) relation and we discuss the possible percolation type of transition in our Si sample.