Extended Data Fig. 4: Landau level spectroscopy of α-As.
From: A hybrid topological quantum state in an elemental solid
a, dI/dV line map (top) and its derivative (bottom) under B = 8 T applied perpendicularly to the cleaved surface. The intense modulation in differential conductance is due to Landau quantization. b, Averaged dI/dV spectra at B = 0 T, and 8 T taken from the same region clarifying that the dI/dV modulation is due to Landau quantization. c, Derivative (to remove the slowly varying background) of the 8 T data and its Fourier transform (inset) showing two (close-by) peaks, suggesting two sets of Landau fans. d, Field-dependent differential conductance data obtained from a line cut of the Landau fan (shown in Fig. 1h) at the Fermi energy. e, Fourier transform of panel d data (after replotting the data as a function of \(\frac{1}{B}\)). Fourier transform magnitude as a function of cyclotron frequency reveals two well-developed peaks at 175 T and 187 T. The two peaks correspond to the Fermi surface areas (in units of cyclotron frequency) of the two Fermi pockets stemming from the Rashba-split surface state. f, Schematic illustration of the Fermi surface stemming from the Rashba bands (see Extended Data Fig. 1c for numerically computed bands). Left: Schematic energy-momentum plot of the parabolic Rashba bands. A cut at the Fermi energy yields two concentric, ring-shaped Fermi pockets. Right: Schematic Fermi surface plot containing the two concentric ring-shaped pockets (see Extended Data Fig. 2c for numerically computed Fermi surfaces). The experimentally obtained 175 T and 187 T peaks (panel e) represent the area of the inner and outer ring-shaped Fermi pockets, respectively. Tunneling junction set-up: Vset = 50 mV, Iset = 0.5 nA, Vmod = 0.5 mV.
