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In a recent experiment, Lai et al. [Phys. Rev. B 75, 033314 (2007)] studiedthe apparent metal-insulator transition (MIT) of a Si quantum well structuretuning the charge carrier concentration $n$. They observed linear temperaturedependences of the conductivity $\sigma(T,n)$ around the Fermi temperature andfound that the corresponding $T \to 0$ extrapolation $\sigma_0(n)$ exhibits asharp bend just at the MIT. Here, reconsidering the data published by Lai etal., it is shown that this sharp bend is related to a peculiarity of$\sigma(T=const.,n)$ clearly detectable in the whole $T$ range up to 4 K, thehighest measuring temperature in that work. Since this peculiarity seems not tobe smoothed out with increasing $T$ it may indicate a sharp continuous phasetransition between the regions of apparent metallic and activated conduction tobe present at finite temperature. Hints from the literature of such a behaviorare discussed. Finally, a scaling analysis illuminates similarities to previousexperiments and provides understanding of the shape of the peculiarity and ofsharp peaks found in $d log_{10} \sigma / d n (n)$.

physical review. b, condensed matter and materials physics

Indications for sharp continuous phase transitions at finite  temperatures connected with the apparent metal-insulator transition in  two-dimensional disordered systems