Extended Data Fig. 6: Helicoid arc unique dispersion in the (001) surface BZ of CoSi.
From: Tunable topologically driven Fermi arc van Hove singularities
a, ARPES measured constant energy contour (top panel) at, within the experimental resolution, the type-II inter-helicoid arc van Hove singularity energy (EVHS). The black dashed lines illustrate the (001) surface Brillouin zone boundary dashed lines. b, Corresponding 2D curvature plot of the data presented in panel (a). Using a standard Lorentzian fitting procedure, the helicoid arc at EVHS is tracked (red circles). c, 2D curvature energy-momentum cuts along orthogonal directions bisecting the inter-helicoid arc van Hove singularity. A saddle-shape dispersion is observed and tracked using a Lorentzian fitting procedure (red circles). d-g, ARPES measured Fermi surface map of the helicoid arcs near the \(\bar{{{{\rm{M}}}}}\)-pocket. The energy-momentum cuts of interest are labeled cut 1 (panel e), cut 2 (panel f), and cut 3 (panel g). The Fermi velocity of the helicoid arc dispersion is extracted along cuts 1, 2, and 3. The grey dots track the dispersion along cuts 1 and 2. A nearly 1D-like dispersion (flat-like band) with an extremely low Fermi velocity obtains along cut 3 (panel g), relative to the high Fermi velocity dispersion along cut 1 (panel e) and cut 2 (panel f).
