Fig. 1. Physical and electronic structure.

(A) Crystal structure of HfSe₂ and ZrSe₂ along with reciprocal unit cell (top) outlining high-symmetry points. In-plane ARPES spectra of in situ vacuum-cleaved, Na doped (B) ZrSe₂ and (C) HfSe₂ reveal a band structure around the VBM (at Γ point) and lower edges of CBM (at M point), along with reciprocal space distributions of degenerate CBM valleys. Dashed red lines are the theoretical band structure from DFT calculations (HSE06 hybrid functional) in the Γ to M direction, adjusted for a ~0.05-eV (~0.12 eV) underestimate for Γ to M energy gaps of ZrSe₂ (HfSe₂).