Effect of long-range potential fluctuations on scaling in the integer quantum Hall effect

We report a set of transport data taken in two low-mobility GaAs/Alₓ{Ga}_{1{{-}}x}$As heterostructures. When T>200 mK, we find that the T dependence of (d${{{ρ}}}xy$/dB${)}ᵐᵃˣ$ behaves differently in different Landau levels, whereas when T200 mK, it behaves like ${T}^{{{-}}0.42}$ as reported by Wei et al. [Phys. Rev. Lett. 61, 1294 (1988)]. The characteristic T (=200 mK) for observing the critical behavior is much lower than that of previous observations in the ${In}ₓGa_1-xAs/InP heterostructure. This lowering of T for scaling is attributed to the dominance of long-range potential fluctuations due to the remote ionized impurities in the Alₓ{Ga}_{1{{-}}x}$As.