Fig. 3: Octdong Fermi surface formed by the nodal line piercing E_F in 3R-TaS₂.

a ARPES and DFT (k_z = 0) Fermi surfaces showing the octdong formed by the hole and electron pockets. b Calculated splitting between the two bands crossing the Fermi level on the mirror plane, showing the presence of a nodal line winding twice around the mirror plane. Panel c show the dispersion along four different directions perpendicular to the mirror plane on both sides of the octdong touching point along the cuts in a, both for the ARPES data and the DFT calculations (k_z = 0). While going from the central hole pocket to the external electron pocket the bands on the mirror plane move from positive to negative binding energies, meaning that the crossing point must also transition from above (red) to below (blue and green) the Fermi level, as predicted for the octdong Fermi surface in ref. ⁶, thus crossing the Fermi level (purple). The dotted lines represent the degenerate bands in the absence of SOC. Notice that in the DFT calculations for the green cut a small splitting of the bands on the mirror plane is visible, but this is simply due to the fact that the nodal line is not exactly at k_z = 0.