Quantum Hall effect in a wide parabolic quantum well

We investigate the activated conductivity for Landau levels at filling factors v=1,2 in a parabolic AlxGa1-xAs well down to 30 mK. We obtain a very small activation energy similar to 0.02 meV, which is almost 1-2 orders of magnitude smaller than the expected values for energy gaps in a wide quantum well. The resistivity minima vanish completely when a parallel component of magnetic field is applied. The collapse of the energy gaps in the wide parabolic well occurs due to the new electron correlated state, probably the charge density wave state predicted for a uniform wide electron slab in high magnetic field.