Fig. 2: In-plane dispersion of spectral function.

a Three-dimensional and projected Brillouin zone of Nb₃Br₈. In the projected surface Brillouin zone (red hexagon), the reciprocal lattice vectors \({a}_{H}^{*}\) and \({c}_{H}^{*}\) are represented in the hexagonal coordinate system. b Room temperature infrared absorption spectrum of Nb₃Br₈ shown as a Tauc plot. The optical bandgap is extracted from the intersection of the leading edge with the baseline. c, d show DFT bandstructures in the Γ- and T-planes, respectively. The in-plane electronic structure of Nb₃Br₈ in the planes e k_z = 0 measured at hv = 85 eV and f k_z = π measured at hv = 67 eV. g, h show zoomed-in valence band maxima in the two k_z planes. The green and red-orange windows show integration windows for EDCs in (i) and (j). The blue curve in i and j are a fit that includes k_z broadening (model described in Supplementary Information). k, l illustrate the in-plane bandwidth (δ_BW) of the VBM in the two k_z-planes, respectively, as extracted from the peaks of the EDCs (indicated by the dashed lines) at the \(\bar{\Gamma }\), and \(\bar{M}\) point.