The Edge-State Theory of Integer-Quantum-Hall-Effect to Insulator   Transition
  Direct transitions, driven by disorder, from several integral quantum Hall states to an insulator have been observed in experiment. This finding is enigmatic in light of a theoretical phase diagram, based on rather general considerations, that predicts a sequence of transitions in which the integer $n$ characterizing the Hall conductivity is reduced successively by unity, eventually going from $n=1$ into an insulator. In this work, we suggest that the direct transition occurs because, in certain parameter regime, the edge states of different Landau levels are strongly coupled and behave as a single edge state. It is indicated under what conditions successive transitions may be seen. 
X. R. Wang, X. C. Xie, Q. Niu, and J. K. Jain