Quadratic nodal line phonon with hybrid type in hexagonal compound SrCuSi

Abstract

Topological phononics emerges as a new research field with the expansion of topological concept from the conventional electronic fermions. Even with a lot of common features, topological phononic states still exhibit many distinct properties. With the continuous development, the current research has even been further extended into high order dispersion conditions. Compared with the traditional linear dispersion, high order topological elements can feature very exotic behaviors, such as high topological charge and chiral surface states, and thus have attracted a lot of research attention. In this work, based on theoretical calculation and effective model analysis, we present an ideal quadratic nodal line phonon in the hexagonal compound SrCuSi. With the symmetry enforced protection, this nodal line also shows an interesting hybrid type combination. Moreover, prominent surface states with large separation from the bulk band can be very beneficial for further experimental investigation. Our theoretical results can immediately advance the relative studies in topological phononics and, especially, the proposed material can put forward an effective way to examine the topological nodal line phonon with quadratic order or hybrid type.