Tunable double Weyl phonons driven by chiral point group symmetry

Abstract

Different from spin-$\frac{1}{2}$ Weyl points which are robust due to the protection of topology, the unconventional chiral quasiparticles usually require extra crystalline symmetries for their existence, indicating that such quasiparticles are sensitive to perturbation. Herein, we present that the spin-1 Weyl can transform into quadratic Weyl phonons depending on symmetry variation. Specifically, the spin-1 Weyl nodes arisen from three-dimensional (3D) irreducible representations (IRs) of chiral point groups, $O$(432) or $T$(23), are verified to split into quadratic Weyl points if symmetry breaking decomposes 3D IRs into two-dimensional IRs. Symmetry analysis and low-energy effective models are performed to identify the splitting mechanisms. The evolution of Berry curvature and surface states driven by symmetry breaking is obtained in real materials. Our work not only builds the connection between double Weyl phonons but also offers guidance for exploring the transition among unconventional quasiparticles.