[Paper Review] Monopole-like orbital-momentum locking and the induced orbital transport in topological chiral semimetals

Qun Yang, Jiewen Xiao+4 more|arXiv (Cornell University)|Jul 5, 2023

Topological Materials and PhenomenaPhysics and Astronomy3 citations

TL;DR

This paper reveals a monopole-like orbital-momentum locking texture on the 3D Fermi surfaces of topological chiral semimetals with B20 structure (e.g., RhSi, PdGa), which induces a large orbital Hall effect (OHE) and a giant, chirality-dependent orbital magnetoelectric (OME) effect under current flow. The OME effect is significantly larger than its spin counterpart, highlighting orbital texture as a key driver for orbitronics and enantiomer recognition applications.

ABSTRACT

The interplay between chirality and topology nurtures many exotic electronic properties. For instance, topological chiral semimetals display multifold chiral fermions that manifest nontrivial topological charge and spin texture. They are an ideal playground for exploring chirality-driven exotic physical phenomena. In this work, we reveal a monopole-like orbital-momentum locking texture on the three-dimensional Fermi surfaces of topological chiral semimetals with B20 structures (e.g., RhSi and PdGa). This orbital texture enables a large orbital Hall effect (OHE) and a giant orbital magnetoelectric (OME) effect in the presence of current flow. Different enantiomers exhibit the same OHE which can be converted to the spin Hall effect by spin-orbit coupling in materials. In contrast, the OME effect is chirality-dependent and much larger than its spin counterpart. Our work reveals the crucial role of orbital texture for understanding OHE and OME effects in topological chiral semimetals and paves the path for applications in orbitronics, spintronics, and enantiomer recognition.

Motivation & Objective

• To investigate the role of orbital texture in topological chiral semimetals with B20 structures such as RhSi and PdGa.
• To understand how chirality and topology jointly influence orbital and spin transport phenomena.
• To explore the emergence of large orbital Hall and orbital magnetoelectric effects driven by unique orbital-momentum locking.
• To distinguish the chirality-dependent nature of the orbital magnetoelectric effect from its spin counterpart.
• To establish the potential of these materials for applications in orbitronics, spintronics, and chiral sensing.

Proposed method

• First-principles electronic structure calculations were performed on B20-type chiral semimetals (RhSi, PdGa) to map the orbital texture on their 3D Fermi surfaces.
• The orbital-momentum locking was identified via analysis of the momentum-space Berry connection and curvature, revealing a monopole-like texture.
• Orbital transport coefficients were computed using the Kubo formula, incorporating orbital matrix elements and Fermi surface anisotropy.
• The orbital Hall effect (OHE) and orbital magnetoelectric (OME) effect were evaluated under applied current and electric fields.
• Spin-orbit coupling was included to examine the conversion of OHE into spin Hall effect in these materials.
• Enantiomer-specific responses were analyzed to confirm the chirality dependence of the OME effect.

Experimental results

Research questions

• RQ1 How does orbital-momentum locking manifest on the 3D Fermi surfaces of topological chiral semimetals with B20 structure?
• RQ2 What is the magnitude and origin of the orbital Hall effect in these materials, and how does it compare to the spin Hall effect?
• RQ3 Is the orbital magnetoelectric effect chiral, and how does its strength compare to the spin counterpart?
• RQ4 Can the orbital Hall effect be converted into a spin Hall effect via spin-orbit coupling?
• RQ5 What is the role of orbital texture in enabling large, chiral, and nontrivial transport responses?

Key findings

• A monopole-like orbital-momentum locking texture is identified on the 3D Fermi surfaces of B20-type chiral semimetals such as RhSi and PdGa.
• This texture leads to a large orbital Hall effect (OHE), with the OHE being identical in magnitude for both enantiomers.
• The orbital magnetoelectric (OME) effect is strongly chiral, with a magnitude significantly larger than the corresponding spin magnetoelectric effect.
• Spin-orbit coupling enables the conversion of the OHE into a spin Hall effect, confirming the interplay between orbital and spin degrees of freedom.
• The orbital texture is the dominant origin of the giant OME effect, distinguishing it from conventional spin-based magnetoelectric responses.
• These findings establish topological chiral semimetals as promising platforms for orbitronics and enantiomer-specific sensing.