a, Berry flux contributions to the lowest two bulk bands, derived from the numerically calculated Weyl charge distributions (see Fig. 2h). Here |C| labels the amplitude of the Weyl charge, and the red and black spheres indicate sources and sinks of Berry fluxes, respectively. b, Chern numbers for the lowest two bulk gaps opened at kz > 0, labelled according to the Berry flux distributions in a. (Here, the band structure is simulated at kz = 0.5π/h.) The Chern numbers Cgap of both gaps are −1, consistent with the topologically non-trivial surface spectra presented in Extended Data Fig. 1.