Fig. 4: Observation of helicoid quantum arcs in CoSi. | Nature

Fig. 4: Observation of helicoid quantum arcs in CoSi.

From: Topological chiral crystals with helicoid-arc quantum states

Fig. 4

a, ARPES spectrum along loop \({\mathscr{P}}\), revealing two right-moving chiral edge modes and a projected chiral charge of −2 at \(\bar{{\rm{M}}}\). Inset, definition of loop \({\mathscr{P}}\), starting from the green mark and proceeding clockwise. b, Lorentzian fits (red lines) to a series of MDCs (blue circles) along \({\mathscr{P}}\) to track the dispersion of the chiral edge modes (orange dashed lines). c, Ab initio calculation of the dispersion along a loop around \(\bar{{\rm{M}}}\), showing two right-moving chiral edge modes, consistent with the ARPES data. Colour scale as in Fig. 1f. d, Extracted dispersion of the chiral edge modes on \({\mathscr{P}}\) and a second inner loop from Lorentzian fits to the MDCs. Error bars correspond to the momentum resolution. Inset, definition of the second inner loop (black). We observe that the chiral edge modes spiral clockwise with decreasing binding energy (approaching EF). e, Perspective plot of d, where the two loops are shown as two concentric cylinders. The winding of the chiral modes around \(\bar{{\rm{M}}}\) as a function of binding energy suggests that the Fermi arcs have a helicoid structure6,27. f, Constant-energy contours calculated ab initio, consistent with the helicoid Fermi arc structure observed in our ARPES spectra.

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