Classical versus Quantum Transport near Quantum Hall Transitions

In attempt to settle the apparent disagreements between different experimental results, transport data near quantum Hall transitions are interpreted by identifying two distinct conduction regimes. The ``classical'' regime, dominated by nearest neighbor hopping between localized conducting puddles, manifests an activated-like resistivity formula, and the quantized Hall insulator behavior. At very low temperatures $T$, or farther from the critical point, a crossover occurs to a "quantum" transport regime dominated by variable range hopping. The latter is characterized by a different T-dependence, yet the dependence on filling fraction is, coincidentally, hard to distinguish.