Figure 2: Electronic dispersion exhibiting back bending.

(a,b) FF divided EDCs as a function of momentum k along cut 1 (defined in d), which is close to the K–M line, for x=0, and at T=26 K and T=50 K, respectively. Red EDCs are associated with momenta k inside the inner Fermi surface (centred around the K point) starting from the brown dot (shown in d) to the red dot along cut 1, green ones to the remaining k points along cut 1 between the red and black dots. (c) FF divided EDCs for x=0.0165 (Co intercalation) at T=18 K, along cut 2, which is along K–M, as shown in d. Red EDCs correspond to k starting from the brown dot inside the inner Fermi surface (centred around the K point) to the pink dot along cut 2, green ones to the remaining k points between the pink and black dots. Blue curves indicate EDCs at the Fermi momentum, the black dots show the locations of the peak and kinks of the EDCs and the black dashed lines are at the chemical potential. The method for locating the black dots is described in Supplementary Note 5 and Supplementary Fig. 7. (d) Fermi surface plot based on the tight-binding fit to the band structure of 2H-NbSe₂ in ref. 24. Black and red arrows denote outer and inner Fermi surface barrels.