Coexistent chiral phonons and multiple topological states with van-Hove singularities in noncentrosymmetric XYZ (X = Ni, Pt, Pd; Y = Sb, Bi; Z = S, Se) family: An ab-initio study.

Non-symmorphic chiral crystals can host unconventional higher-fold topological excitations with long Fermi arcs. On the other hand, phonons in chiral materials possess a non-zero angular momentum, leading to the generation of chiral phonons. This work reports the coexistence of higher-fold topological and chiral phonons, accompanied by multiple types of conventional and unconventional fermions in ternary chiral crystals XYZ (X = Ni, Pt, Pd; Y = Sb, Bi; Z = S, Se). Our detailed study reveals symmetry-protected spin-1 Weyl and charge-2 Dirac topological phonon states in the phonon spectrum, as well as nonzero phonon angular momentum, thereby confirming their chiral nature. Interestingly, the electronic states exhibit multiple types of topological fermionic states under spin-orbit coupling (SOC). Moreover, a close examination of the density of states reveals van Hove singularities near the Fermi level, which may indicate possible superconductivity and warrant further experimental studies. Our findings highlight the coexistence of chiral and higher-fold topological phonons, multiple topological states in both phononic and electronic realms, and van Hove singularities in the studied ternary chiral crystals, which may serve as a basis for future topological device applications.