Fermi surface of the chiral topological semimetal CoSi

TL;DR

This study combines experimental and computational methods to map the Fermi surface of CoSi, revealing its complex topological features and the influence of multifold crossings, Weyl points, and nodal planes on its electronic structure.

Contribution

It provides a detailed experimental and theoretical analysis of CoSi's Fermi surface, highlighting the complex network of topological crossings and their topological protections.

Findings

Identified two main Fermi-surface sheets at R and Γ points.

Found topological nodal planes enforce protections on certain Fermi surfaces.

Located Weyl points near the Fermi-surface sheets.

Abstract

We report a study of the Fermi surface of the chiral semimetal CoSi and its relationship to a network of multifold topological crossing points,Weyl points, and topological nodal planes in the electronic band structure. Combining quantum oscillations in the Hall resistivity, magnetization, and torque magnetization with ab initio electronic structure calculations, we identify two groups of Fermi-surface sheets, one centered at the R point and the other centered at the $\Gamma$ point. The presence of topological nodal planes at the Brillouin zone boundary enforces topological protectorates on the Fermi-surface sheets centered at the R point. In addition, Weyl points exist close to the Fermi-surface sheets centered at the R and the $\Gamma$ points. In contrast, topological crossing points at the R point and the $\Gamma$ point, which have been advertised to feature exceptionally large Chern numbers, are located at a larger distance to the Fermi level. Representing a unique example in which the multitude of topological band crossings has been shown to form a complex network, our observations in CoSi highlight the need for detailed numerical calculations of the Berry curvature at the Fermi level, regardless of the putative existence and the possible character of topological band crossings in the band structure.