Hourglass nodal ring phonons in two-dimensional LiHS

Exploration of topological phonons in two-dimensional (2D) has long been regarded as one of the central topics in topological physics. Due to their distinct band dispersion, hourglass nodal rings have garnered considerable attention, but their existence in 2D materials, particularly in spinless phonon systems, has received scant attention. Using the first-principle calculations, this study shows that P4/nmm type LiHS monolayer is an ideal candidate for hosting hourglass nodal ring phonons. Moreover, the phononic edge states induced by the nodal ring phonons in LiHS are also exhibited in this work. Our work provides the first 2D material candidate to study hourglass nodal ring phonons and the phononic edge states induced by the nodal ring phonons.