ABSTRACT
We first discuss longitudinal resistances at B < 0.1 T where negative magnetoresistances survive for any gate voltages. It is well known that weak localization gives rise to negative magnetoresistance at low fields, as often seen in 2DEG system with weak disorder. To get deeper insight, we converted resistance to conductance G(B) and plotted in Fig.3 AG (=G(B)-G(0)) perpendicular and parallel to the steps for Vg = 0 and -0.4 V. The magnetoconductance for J across the step AG (AGx) depend on Vg, while those AGy for parallel direction are less dependent on Vg. According to Ref.6 , anisotropic diffusion in lateral superlattices enhances weak localization for the parallel direction and reduces it for the perpendicular direction. Hence, the ratio of A G r ( = A G x / AGy) depends on the ratio of the diffusion constant D [6 ]. In our sample Dx/Dy derived from the mobility ratio is between 10 to 4 for Vg ranging from -0.4 to 0 V From the Vg dependence of A G r at B < 0.1 T, we suggest that negative magnetoresistance seen at B below 0.1T is caused by the weak localization.
