Hopping Conductivity in the Quantum Hall Effect: Revival of Universal Scaling

We have measured the temperature dependence of the conductivity σₓₓ of a two-dimensional electron system deep into the localized regime of the quantum Hall plateau transition. Using variable-range hopping theory we extract directly the localization length ξ from this experiment. We use our results to study the scaling behavior of ξ as a function of the filling factor distance |δν| to the critical point of the transition. We find for all samples a power-law behavior ξ∝|δν|^-γ in agreement with the theoretically proposed universal exponent γ0ex0ex=0ex0ex2.35.