Topological Semimetal in a Chiral Crystal with Large Chern Numbers, Multifold Band Crossings, and Long Fermi-arcs

Topological semimetals (TSs) in structurally chiral crystals (which possess a handedness due to
a lack of mirror and inversion symmetries) are expected to display numerous exotic physical
phenomena, such as new fermionic excitations with large topological charge, long Fermi-arc
surface states, unusual magnetotransport and lattice dynamics, as well as a quantized response
to circularly polarized light. Despite multiple recent photoemission studies of predicted material
candidates, this maximal Chern number, measured by counting the number of Fermi-arcs, has
not yet been observed experimentally. Using angle-resolved photoelectron spectroscopy and ab-
initio calculations, here we show that the chiral topological semimetal candidate PdGa displays
the required multifold nodes, which are connected by long surface Fermi-arcs. Due to large spin-
orbit coupling and the high crystallinity of our sample surfaces, we are for the first time able to
resolve 4 independent Fermi-arcs, proving experimentally that the observed multifold nodes –
which are a generic feature of many chiral metals – display the maximal Chern number
magnitude of 4.

****See continuation in Special Instructions.........