Fermiology of two-dimensional lateral superlattices

We present magnetotransport experiments on high mobility two-dimensional el ectron systems subjected to a weak, short period superlattice potential. Th e imposed periodic potential modifies the contours of constant energy of th e free electrons such that new closed k-space trajectories, involving magne tic breakdown, become possible. Their existence is heralded by a novel type of low-field quantum oscillations.