Fig. 4.

Iso-energetic mapping of the type-II Dirac fermions. a Fermi surface map of La_1.77Sr_0.23CuO₄ (no symmetrisation applied). Blue and purple circles, respectively, indicate the momentum positions of the equivalent Dirac points. b–i Constant-energy surfaces at binding energies as indicated. Each panel shows the experimental map (right) and the tight-binding surface colour-coded according to the orbital character (left). The maps have been symmetrised assuming four-fold rotational symmetry and mirror symmetry with respect to the diagonal direction. j Sketch of the three-dimensional Brillouin zone. k Tight-binding band dispersion along the diagonal cuts indicated in panels a and j. Dotted lines indicate the selected constant-energy maps shown in b–i. l Schematic plot of the present type-II Dirac cone in energy—k_x−k_y space at k_z = 0