Fig. 3: Electronic structures of the (100) planes of Bi4(Br1-xIx)4 crystals.
From: Coalescence of multiple topological orders in quasi-one-dimensional bismuth halide chains
a E-ky-kz dispersion spectra measured at the in-situ-cleaved (100) surfaces of Bi4(Br1-xIx)4 crystals with x ranging from 0 to 1(from left to right). The inset indicates the experimental setup for the (100) surface characterization. The red dot and pink dot represent the (100) projected \(\bar{\Gamma }\) point and \(\bar{{{{\rm{Z}}}}}\) point, respectively. b, c High-resolution E-ky dispersions at the \(\bar{\Gamma }\) point and \(\bar{{{{\rm{Z}}}}}\) point, respectively. The yellow dashed lines are guides to the eye for the surface state dispersion. The coupling gap \({\varDelta }_{S}\) is indicated by the white dashed line. There are two nondegenerate Dirac points (DPs) at both the \(\bar{\Gamma }\) point and the \(\bar{{{{\rm{Z}}}}}\) points for I concentrations of 0%, 25%, 62%, and 100%. The Bi4(B0.5I0.5)4 crystal exhibits a triple-layer unit cell and is identified as a weak topological insulator (WTI)36. The crystal with 80% I content, however, shows double DPs at the \(\bar{\Gamma }\) point but a single DP at the \(\bar{{{{\rm{Z}}}}}\) point (labeled by a yellow arrow). The bottom orange arrow denotes the I concentration.
