Coexistence of multifold and multidimensional topological phonons in KMgBO3

Topological interpretations of phonons facilitate a platform for unique concepts in phonon physics. Though there are ubiquitous reports on topological electronic excitations, the same for phonons is extremely limited. Here, we propose a candidate material, KMgBO3, which showcases the coexistence of several multifold and multidimensional topological phonon excitations, which are protected by spatial and nonspatial symmetries. This includes zero-dimensional double, triple, and quadratic Weyl phonon nodes, one-dimensional nodal line/loops, and two-dimensional doubly degenerate nodal surface states. The nodal line/loop emerges from the spin-12 phonon nodes, while the two-dimensional doubly degenerate nodal surface arises from a combination of twofold screw-rotational and time-reversal symmetries. Application of strain breaks the C3 rotational symmetry, which destroys the spin-1 double Weyl nodes but preserves other topological features. Interestingly, strain helps create two extra single Weyl nodes, which in turn preserve the total chirality. Alloying also breaks certain symmetries, destroying most of the topological phonon features in the present case. Thus, KMgBO3 is a promising candidate which hosts various Weyl points, large Fermi arcs with very clean phonon spectra, and tunable topological phonon excitations, and hence is certainly worth future theoretical/experimental investigation of topological phononics.