Chirality is ubiquitous in nature and manifests in a wide range of phenomena

including chemical reactions, biological processes, and quantum transport

of electrons. In quantum materials, the chirality of fermions, given by the

relative directions between the electron spin and momentum, is connected

to the band topology of electronic states. This study shows that in structurally

chiral materials like CoSi, the orbital angular momentum (OAM) serves as the

main driver of a nontrivial band topology in this new class of unconventional

topological semimetals, even when spin-orbit coupling is negligible.

A nontrivial orbital-momentum locking of multifold chiral fermions in

the bulk leads to a pronounced OAM texture of the helicoid Fermi arcs at the

surface. The study highlights the pivotal role of the orbital degree of freedom

for the chirality and topology of electron states, in general, and paves the way

towards the application of topological chiral semimetals in orbitronic devices.

‍