Indications for a line of continuous phase transitions at finite temperatures connected with the apparent metal–insulator transition in 2d disordered systems

In a recent experiment, Lai et al. [Phys. Rev. B 75 (2007) 033314] studied the apparent metal–insulator transition (MIT) of a Si quantum well structure. Tuning the charge carrier concentration n, they measured the conductivity σ(T,n) for a very dense set of n values. They observed linear T dependences of σ around the Fermi temperature and found that the corresponding T→0 extrapolation σ0(n) exhibits a sharp bend just at the MIT. Reconsidering the data by Lai et al., it is shown here that this sharp bend is related to a peculiarity of σ(T=const.,n), which is clearly detectable in the whole T range up to 4 K, the highest measuring temperature in that work. It may indicate a sharp continuous phase transition between the regions of apparent metallic and activated conduction to be present at finite temperature. This interpretation is confirmed by a scaling analysis without fit, which illuminates similarities to previous experiments and provides understanding of the shape of the peculiarity and of sharp peaks found in View the MathML source. Simultaneously, the scaling analysis uncovers a strange feature of the apparent metallic state.