Extended Data Fig. 6: Frequency-dependent surface dispersion and robustness of chiral surface states.

a, c, Measured surface dispersions on the frontal (010) surface of the fabricated sample in Fig. 2 for B = 0.20 T and 0.45 T, respectively. Three values of k_z = 0, 0.53π/h, and 1π/h are selected. b, d, Simulated band structure on the frontal (010) surface for B = 0.20 T and 0.45 T, respectively. The white and green curves in a and c indicate the simulated envelopes of the projected bulk dispersions and surface dispersions, respectively. The blue curved surfaces in b and d represent the topological surface states, while the orange sheets indicate the envelopes of the projected bulk dispersions. e, Measured field distribution of chiral surface states in the fabricated sample in Fig. 2. The surface states are excited by a point source (cyan star) oscillating at 19.6 GHz. f, Measured field distribution in the same setup as in e, while copper pillars (yellow rods) are inserted into the sample as metallic obstacles. The frontal (010), left (100), and right (100) surfaces of the sample are covered with copper claddings, and all other surfaces with microwave absorbers. The samples are biased at 0.45 T along +z axis. The chiral surface states can propagate smoothly around the sharp corners and obstacles without scattering. The surface waves are mainly confined at their individual layers when passing around the copper pillars due to the weak dispersion along the z-axis.