Orbital Topology of Chiral Crystals for Orbitronics

TL;DR

This paper reveals that in chiral materials like CoSi, orbital angular momentum primarily drives nontrivial band topology, influencing surface states and enabling potential orbitronic device applications.

Contribution

It demonstrates that orbital angular momentum, rather than spin-orbit coupling, governs the topological properties of chiral semimetals like CoSi.

Findings

Orbital angular momentum is the main driver of band topology in CoSi.

Nontrivial orbital-momentum locking leads to distinctive surface Fermi arcs.

Orbital degree of freedom is crucial for chirality and topology in electron states.

Abstract

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. Here, we show 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. Our findings highlight the pivotal role of the orbital degree of freedom for the chirality and topology of electron states, in general, and pave the way towards the application of topological chiral semimetals in orbitronic devices.