Fig. 3: Observation of topological Fermi arcs and chiral charges in PrAlGe.

a Bulk and surface Brillouin zone (BZ) with the Weyl fermions (±) and manifolds with Chern number n³². A closed loop enclosing the projected chiral charge in the surface corresponds to a cylinder in the bulk enclosing the Weyl fermion. b Top: topological Fermi arcs (orange) connecting the projected Weyl fermions carrying chiral charge  ±1. Bottom: a cut across two arcs (along the black line in top panel) with chiral edge modes (orange lines). c Top panel: Fermi surface obtained by ARPES at T ≈ 11K. Loop cuts of interest (P and M) are illustrated with black loops with the starting/end points marked by the vertical blue line. Bottom panel: 2D curvature plot of the above Fermi surface. d Measured band dispersion along horizontal Cut I. Blue dashed line: indicates the mirror symmetry. e Second-derivative plot of d. f ARPES-measured band dispersion along the loop P. Loop P encloses the termination point of the measured Fermi arc and shows a single left-moving chiral mode, corresponding to an enclosed Chern number n = −1. g Band dispersion along loop M. The observed right-moving chiral mode shows an enclosed Chern number n = +1. h Stack of MDCs along loop M at different binding energies, with Lorentzian fits. Green dashed line: guide to the eye tracking the peaks. i Calculated energy dispersion along k_y = −0.25 (2π/a) with the result from our ARPES spectra overlaid (open green circles).