Giant magnetoresistance in lateral surface superlattices

We investigate the low-field magnetoresistance ${\mathrm{\rho }}_{\mathit{xx}}$ perpendicular to a one-dimensional periodic potential which is imposed upon a two-dimensional electron gas in GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunctions. Distinct low-field anomalies and a crossover from positive to large negative magnetoresistance with increasing potential strength unveil the important role of anisotropic relaxation processes in strongly modulated electron systems.