Quantization and chiral edge state properties in nearly 3D quantum well structures

We report magneto-transport measurements including Hall, R-xy, longitudinal , R-xx, and vertical, R-zz, magnetoresistance on nearly 3-dimensional (3D) 200 layer GaAs/AlGaAs quantum well structures. Although the interlayer band width is nearly 20% of the Fermi energy, we still observe complete quantiza tion of the Hall resistance for the 3D quantum Hall state. The temperature dependence of the R-xx minimum shows two unusual features: initially, at hi gher temperatures 1 K where the quantum Hall state develops, a gap with an activation energy much smaller than the Landau gap is observed; in the low temperature limit 0.030 K a variable range hopping behavior takes over with a residual resistivity limit. Independent measurements of G(zz) (in 3D app roximate to 1/R-zz) where the chiral edge states dominate the vertical tran sport show the same temperature dependence. (C) 1998 Published by Elsevier Science B.V. All rights reserved.