Fig. 3: Observation of topological chiral edge modes in CoSi. | Nature

Fig. 3: Observation of topological chiral edge modes in CoSi.

From: Topological chiral crystals with helicoid-arc quantum states

Fig. 3

a, Left panel, schematic of three-dimensional bulk and two-dimensional surface BZ of CoSi with chiral fermions marked (±) and including several examples of two-dimensional manifolds hosting a Chern number n (green planes, red cylinder)33. Every plane in the bulk has a non-zero n. The cylinder enclosing the bulk chiral fermion at Γ has n = +2. Right panel, Fermi arcs (orange curves) show up as chiral edge modes (orange lines). Energy–momentum cuts (k||) on opposite sides of \(\bar{{\rm{\Gamma }}}\) are expected to show chiral modes propagating in opposite directions. b, ARPES spectrum along cut I (as marked in Fig. 2f), suggesting two right-moving chiral edge modes (black arrows). Vertical dashed lines mark the BZ boundaries. c, Second-derivative plot of cut I, with fitted Lorentzian peaks (blue dots) for a series of MDCs to track the dispersion. d, MDCs (blue circles) and Lorentzian fits (red lines) tracking the chiral edge modes (orange dashed lines) for cut I. e, Same as b, but for cut II, suggesting two left-moving chiral edge modes (black arrows). f, Same as c, but for cut II. The difference in the net number of chiral edge modes on cut I and cut II suggests a Chern number of +2 near \(\bar{{\rm{\Gamma }}}\).

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