WIDTHS OF PLATEAUS IN THE INTEGRAL QUANTUM HALL-EFFECT OF GAAS/ALGAAS HETEROSTRUCTURES

The integral quantum Hall effect of two-dimensional electron systems is studied for a GaAs/AlGaAs heterostructure with electron densities n(s) = 2.5 x 10(11) cm(-2) at 0.1 K and 4.2 K and with magnetic fields ranging from 0 to 10 T. Landau-level filling up to the filling number nu = 12 can be clearly seen at 0.1 K. In addition to the typical variations with magnetic field in the longitudinal and transverse resistances, R(xx) and R(xy), respectively, we find the plateau in R(xy) is wider when nu is even than when it is odd. The peaks in R(xx) are also larger when nu is increased from odd to even integers than when it changes from even to odd. Similar features: but with less clear plateaus and peaks in the resistances, are observed at 4.2 K. The saturated width Delta nu of the even Landau levels is 1.4 +/- 0.1, which is much larger than the predicted 2 nu(c) where the critical value for melting of a Wigner solid is nu(c) congruent to 0.2.