For each device, the optical image is shown at the top and the corresponding model shown under. a, Control device C1. b, Asymmetric device A1. c, Symmetric device S1. d, Another symmetric device with a single-sided region. Details about this device are presented in Extended Data Fig. 9. e, Another asymmetric device, A3. This device showed additional features in the magnetocapacitance measurements that are associated with a moiré superlattice potential due to alignment of the BLG with the top hBN, see Extended Data Fig. 7.