Insulator-quantum Hall conductor transition in high electron density gated InGaAs/InAlAs quantum wells

We study the insulator-quantum Hall conductor transition in two high-density gated InGaAs/InAlAs quantum well samples. We observe a well-defined critical magnetic field and verify this marks a genuine phase transition by investigating the scaling behavior of the longitudinal resistivity with field and temperature at fixed electron density. Consistent with prevailing experimental results the critical field decreases with increasing electron density in one sample (QW0710). In the other sample (QW0715), with higher delta doping density, however, we unexpectedly find that the critical field increases with increasing electron density. This unexpected behavior may be the result of the system entering the classical percolation regime.