Anomalous quadrupole topological insulators in two-dimensional nonsymmorphic sonic crystals
Anomalous quadrupole topological insulators in two-dimensional nonsymmorphic sonic crystals
The discovery of quadrupole topology opens a new horizon in the study of topological phenomena. However, the existing experimental realizations of quadrupole topological insulators in symmorphic lattices with $\pi$-fluxes often break the protective mirror symmetry. Here, we present a theory for anomalous quadrupole topological insulators in nonsymmorphic crystals without flux, …