Phonon Weyl points and chiral edge modes with unconventional Fermi arcs in NbSi$_{2}$

Abstract

NbSi$_{2}$ crystallizes in the P6$_{2}$22 symmetry, featuring chiral chains of Si atoms. The absence of inversion symmetry, combined with its chiral structure, gives arise to unique physical properties. The breaking of inversion symmetry leads to the emergence of Weyl points, while the chiral structure enables the formation of chiral edge modes. As a result, NbSi$_{2}$ serves as an ideal platform for exploring the interplay between phonon Weyl points and chiral phonon edge modes. For example, we identify the presence of a structure consisting of three Weyl points with a Chern number of $\mathcal{C} = +1$ around the $\bar{\text{K}}$ point. These nodes form unconventional Fermi arcs connecting the $\bar{\Gamma}$ or $\bar{\text{K}}$ points, which mimic an effective Chern number of $\mathcal{C} = -2$.