be interesting to estimate coupling constants from the neutron scattering data.

The peak at 950 cm$^{-1}$ is clearly from the inter-band transition between the bands of interest that would host the Weyl nodes in the canted structure i.e., right above (39,40) and below (37,38). However, because of the other low energy transition, it is nearly impossible to isolate any signature of the Weyl nodes if they exist in the optical conductivity spectrum. The peak derives from the quasi-2D Bi $p$-states (see Supplementary Materials) and is indicative of the linear dispersion. A sharp peak in conductivity is ordinarily expected to appear if a pair of occupied initial and empty final bands have nearly parallel dispersion in a large volume in $k$-space. Such an energy dispersion may occur if the Fermi level is inside a gap, which opens due to avoided crossing of two bands, and the size of the gap is constant in a large part of Brillouin zone. Hence it is reasonable to conclude that this peak is a signature of a Dirac dispersion with a small mass gap. This gap between the “lens” shaped Fermi surfaces from the (37,38) bands and the “boomerang” shaped Fermi surfaces from the (39,40) 