No abstract

The temperature driven flow lines of the diagonal and Hall magnetoconductance data (Gxx, Gxy) are studied in heavily Si-doped, disordered GaAs layers with different thicknesses. The flow lines are quantitatively well described by a recent universal scaling theory developed for the case of duality symmetry. The separatrix Gxy = 1 (in units e 2 /h) separates an insulating state from a spin-degenerate quantum Hall effect (QHE) state. The merging into the insulator or the QHE state at low temperatures happens along a semicircle separatrix G 2 xx + (Gxy − 1) 2 = 1 which is divided by an unstable fixed point at (Gxx, Gxy) = (1, 1).

The temperature driven flow lines of the Hall and dissipative magnetoconductance data (σxy, σxx) are studied in the fractional quantum Hall regime for a 2D electron system in GaAs/AlxGa1−xAs heterostructures. The flow lines are rather well described by a recent unified scaling theory developed for both the integer and the fractional quantum Hall effect in a totally spin-polarized 2D electron system which predicts that one (σxy, σxx) point determines a complete flow line.