Probing current and temperature effects on the direct insulator-quantum Hall transition

We report a magneto-transport study on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. The direct insulator-quantum Hall transition is observed at different temperatures by increasing the magnetic field $B$ perpendicular to the 2DES. Such a transition can also be observed by varying the current $I$ since the electron temperature is given by $T _{e} = CI ^{\alpha}$ in both the insulator and quantum Hall sides of the transition. Here $\alpha$ denotes the exponent for the power law and $C$ is a constant at a particular magnetic field. The value of $\alpha$ may be determined by comparing the temperature and current dependences. Our results show that $\alpha$ takes on different values on either sides of the transition point, indicating the presence of different heating mechanisms in the low-field insulator and in the quantum Hall liquid. The effects due to electron-electron interaction and scattering are also discussed.