Extended Data Fig. 4: Photon energy dependence of dark states.
From: Dark states of electrons in a quantum system with two pairs of sublattices
a, Alternating relative phases of PdSe2 between kz = Γ2n and Γ2n+1. b,c, Photon-energy dependence of ARPES data taken at kxy = Γ10 (b) and Γ01 (c), as indicated by dotted arrows in a (p-pol + s-pol, xz scattering plane). The colour scale is normalised based on the background with respect to those taken at kxy = Γ00 (Extended Data Fig. 2a, b), as shown in d. d, Momentum distribution curves taken at E = −0.1 eV along kz (80−200 eV) to make a comparison for those at Γ10, Γ01, and Γ00. e-g, Line profiles taken at 4 different Γhkl points collected to separately show the photon-energy dependence of red (e), yellow (f), and green (g) states corresponding to dark states. As seen in d-g, we find little photon-energy dependence of dark states for all photon energies used here. This is because multiple Coulomb wavelets become simplified (or polarised) into only four kinds in materials with two pairs of sublattices connected by glide-mirror symmetries. Then, the selection rule becomes as stringent as in atomic systems since the role of orbital angular momentum properties is replaced by the equally well-defined sublattice degree of freedom. Namely, this is a consequence of such fully polarised initial state wavefunctions, which has nothing to do with final states, and hence no dependence on photon energies.
