Topological quantum number and critical exponent from conductance   fluctuations at the quantum Hall plateau transition
  The conductance of a two-dimensional electron gas at the transition from one quantum Hall plateau to the next has sample-specific fluctuations as a function of magnetic field and Fermi energy. Here we identify a universal feature of these mesoscopic fluctuations in a Corbino geometry: The amplitude of the magnetoconductance oscillations has an e^2/h resonance in the transition region, signaling a change in the topological quantum number of the insulating bulk. This resonance provides a signed scaling variable for the critical exponent of the phase transition (distinct from existing positive definite scaling variables). 
I. C. Fulga, F. Hassler, A. R. Akhmerov, C. W. J. Beenakker
cond-mat.mes-hall