A study on the universality of the magnetic-field-induced phase   transitions in the two-dimensional electron system in an AlGaAs/GaAs   heterostructure
  Plateau-plateau (P-P) and insulator-quantum Hall conductor (I-QH) transitions are observed in the two-dimensional electron system in an AlGaAs/GaAs heterostructure. At high fields, the critical conductivities are not of the expected universal values and the temperature-dependence of the width of the P-P transition does not follow the universal scaling. However, the semicircle law still holds, and universal scaling behavior was found in the P-P transition after mapping it to the I-QH transition by the Landau-level addition transformation. We pointed out that in order to get a correct critical exponent, it is essential that the scaling analysis must be performed near the critical point. And with proper analysis, we found that the P-P transition and the insulator quantum Hall conductor transitions are of the same universal class. 
C. F. Huang, Y. H. Chang, H. H. Cheng, C. -T. Liang, and G. J. Hwang