a, b, Bulk quantum oscillations in samples 2 (a) and 3 (b) with the magnetic field applied in-plane. The oscillation positions are symmetric in B and there is no shift between the two curves, which helps to exclude changes in the bulk band with thickness as the origin of the Landau-level shift. c, Rxx measured at terminals 2–4 at different temperatures, which is also asymmetric under magnetic fields, similarly to Fig. 3e. The arrow marks the large oscillation peak, which is detected in Rxy (Fig. 3e) at the same field. d, Hall resistance measured at two sets of Hall terminals along the x axis with the same thickness profile. The inset shows an optical image of the Hall bar device with terminals indexed; scale bar, 15 μm.