Fig. 4
From: Quantized surface transport in topological Dirac semimetal films
Gate-modulation of the surface quantum Hall state. a Gate-voltage VG scans of transverse magnetoresistance (MR) at representative fields (B = 4, 8, and 9 T) for a x = 0.19 sample with t = 95 nm. Application of a negative bias (VG < 0) corresponds to the depletion of electrons in the film. With negatively increasing VG, Surface QH states develop with quantization in Hall resistance Ryx (right axis). b, c Contour mapping of the second derivative of transverse MR and longitudinal MR plotted as a function of VG and B. In the transverse MR, the surface QH effect starts to dominate the bulk conduction with reducing the electron density, while only the bulk Landau levels are observed in the longitudinal MR. The QH states are initially characterized by a degeneracy of 4, which is reduced to 2 and finally to 1 with increasing VG (<0) and/or B
