Straight and twisted Weyl nodal line phonons in Ho₂CF₂ material

Based on first-principles calculations, symmetry analysis and model construction, we predict that Ho₂CF₂ hosts both straight and twisted Weyl nodal lines in its bulk phonon spectrum. We identify that the top two phonon bands entangle with each other, forming two straight Weyl nodal lines on the K–H and K′–H′ paths at the Brillouin zone (BZ) boundary, and six twisted Weyl nodal lines within the BZ. All the Weyl nodal lines along the k_z direction and across the entire BZ. The symmetry analysis indicates that these Weyl nodal lines are protected by the $\mathcal{P}\mathcal{T}$ symmetry and crystal symmetry. The Berry phase and drumhead-like nontrivial surface states are calculated. We also construct a tight-binding model to describe these nodal lines. Our work provides an excellent material platform for exploring the fascinating physics associated with straight and twisted Weyl nodal line phonons.