Activation Energies of the 1/3 and 2/3 Fractional Quantum Hall Effect in GaAs/AlxGa1-xAs Heterostructures

Activation energies of the diagonal resistivity ρ x x near the minima in the 1/3 and 2/3 fractional quantum Hall effect are determined in very high mobility GaAs/Al x Ga 1- x As ( x ≃0.3) heterostructures. Measurements of ρ x x and ρ x y are made at temperatures ranging from 1 K to 0.1 K in magnetic fields up to 15.5 T. The activation energies are 2.7 K and 0.89 K at the filling factor of a Landau level of 1/3 and 2/3, respectively. The former is in good agreement with theoretical predictions.