Magneto-quantumtransport on GaAs-AlxGa1?xAs heterostructures at very low temperatures

Magnetoresistance (ρxx) and Hall resistance (ρxy) measurements on GaAs-Al_xGa_1?xAs heterostructures demonstrate that in the temperature limit T → 0 not all states of a Landau level are localized. Moreover, at T < 35 mK one of our devices shows a splitting into three peaks for each spin-split level with Landau quantum number n = 1. This phenomenon seems to be related to the recently observed structures in ρxx and ρxy in the extreme quantum limit which has been tentatively explained as a formation of a new electronic state such as Wigner solid or charge density wave with a triangular symmetry.