# Multiple types of topological fermions in transition metal silicides

## TL;DR

This paper predicts and confirms the coexistence of various unconventional topological fermions, including spin-1 and spin-3/2 excitations, with Weyl fermions in transition metal silicides, revealing rich topological surface states.

## Contribution

It demonstrates, through ab initio calculations, the presence of multiple types of topological fermions in transition metal silicides, expanding the understanding of topological quasiparticles in real materials.

## Key findings

- Coexistence of multiple topological fermions in CoSi, RhSi, RhGe, and CoGe.
- Observation of extensive Fermi arcs connecting bulk excitations.
- Stable arc states within a wide energy window around the Fermi level.

## Abstract

Exotic massless fermionic excitations with non-zero Berry flux, other than Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as spin-1 excitations with 3-fold degeneracy and spin-3/2 Rarita-Schwinger-Weyl fermions. Herein, by using ab initio density functional theory, we show that these unconventional quasiparticles coexist with type-I and type-II Weyl fermions in a family of transition metal silicides, including CoSi, RhSi, RhGe and CoGe, when the spin-orbit coupling (SOC) is considered. Their non-trivial topology results in a series of extensive Fermi arcs connecting projections of these bulk excitations on side surface, which is confirmed by (010) surface electronic spectra of CoSi. In addition, these stable arc states exist within a wide energy window around the Fermi level, which makes them readily accessible in angle-resolved photoemission spectroscopy measurements.