SCALING IN SPIN-DEGENERATE LANDAU-LEVELS IN THE INTEGER QUANTUM HALL-EFFECT

In a low-mobility InxGa1-xAs/InP heterostructure, we find that the quantized Hall resistance plateau, rho(xy) = h/ie2 with i = 3, starts developing only when T is below 50 mK. For higher T, the plateau and the associated minimum in the diagonal resistivity p. can be made to appear by tilting the sample with respect to the B field. We have studied the T dependence of the p. minimum and deduced the thermal-activation energy (A). We find that A is 67 times smaller than the Landau-level broadening deduced from the electron mobility. This result implies that there is no gap in the density of states and that, for T > 50 mK, the Landau level is spin degenerate. In this higher T range, we observe a T-0.21 power law for the maximum value of drho(xy)/dB between the i = 2 and 4 plateaus, and T-0.42 for the minimum value of d2prho(xx)/dB2. These exponents are a factor 2 smaller than those for spin-polarized levels.