Indications for sharp continuous phase transitions at finite
temperatures connected with the apparent metal-insulator transition in
two-dimensional disordered systems
In a recent experiment, Lai et al. [Phys. Rev. B 75, 033314 (2007)] studied
the apparent metal-insulator transition (MIT) of a Si quantum well structure
tuning the charge carrier concentration n. They observed linear temperature
dependences of the conductivity σ(T,n) around the Fermi temperature and
found that the corresponding T→0 extrapolation σ0(n) exhibits a
sharp bend just at the MIT. Here, reconsidering the data published by Lai et
al., it is shown that this sharp bend is related to a peculiarity of
σ(T=const.,n) clearly detectable in the whole T range up to 4 K, the
highest measuring temperature in that work. Since this peculiarity seems not to
be smoothed out with increasing T it may indicate a sharp continuous phase
transition between the regions of apparent metallic and activated conduction to
be present at finite temperature. Hints from the literature of such a behavior
are discussed. Finally, a scaling analysis illuminates similarities to previous
experiments and provides understanding of the shape of the peculiarity and of
sharp peaks found in dlog10σ/dn(n).Comment: Revised version (quantitative determination of exponent beta added),
accepted for publication by Physical Review B. Revtex, 10 pages, 9 figure