On different mobilities in the low-field insulator-quantum Hall transition

We report that the quantum mobility (determined from the Shubnikov-de Haas oscillations) can be much smaller than the Drude mobility (determined from the crossing point) when there exists an approximately temperature ($T$)-independent point in $\rho_{xx}$ for which the corresponding Landau level filling factor $\nu \geq 3$ [1]. Moreover, recently it has been pointed out that the mobility can be renormalized and increases with increasing $T$ [2]. Our experimental results, together with the seminal paper [2] strongly suggest that different mobilities should be considered in the low-field insulator-quantum Hall (I- QH) transition. Most importantly, corrections to the argument raised by Huckestein must be made to obtain a correct insight into the direct low-field I-QH transition [1]. \newline \newline [1] B Huckestein, PRL 81, 3141 (2000) and references therein. \newline [2] G M Minkov et al., PRB 74, 045314 (2006).