Universal flow diagram for the magnetoconductance in disordered GaAs layers

The temperature driven flow lines of the diagonal and Hall magnetoconductance data (G_{xx},G_{xy}) 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 G_{xy}=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_{xx}^2+(G_{xy}-1)^2=1 which is divided by an unstable fixed point at (G_{xx},G_{xy})=(1,1).Comment: 10 pages, 5 figures, submitted to Phys. Rev. Let

Quantum Hall Effect induced by electron-electron interaction in disordered GaAs layers with 3D spectrum

It is shown that the observed Quantum Hall Effect in epitaxial layers of heavily doped n-type GaAs with thickness (50-140 nm) larger the mean free path of the conduction electrons (15-30 nm) and, therefore, with a three-dimensional single-particle spectrum is induced by the electron-electron interaction. The Hall resistance R_xy of the thinnest sample reveals a wide plateau at small activation energy E_a=0.4 K found in the temperature dependence of the transverse resistance R_xx. The different minima in the transverse conductance G_xx of the different samples show a universal temperature dependence (logarithmic in a large range of rescaled temperatures T/T_0) which is reminiscent of electron-electron-interaction effects in coherent diffusive transport.Comment: 6 pages, 3 figures, 1 tabl