Higher-order topology and corner triplon excitations in two-dimensional quantum spin-dimer models

The concept of free fermion topology has been generalized to $d$-dimensional phases that exhibit $(d\ensuremath{-}n)$-dimensional boundary modes, such as zero-dimensional (0D) corner excitations. Motivated by recent extensions these ideas magnetic systems, we consider 2D quantum paramagnets formed interacting spin dimers with dispersive triplet We propose two examples dimer models, where the spin-gapped bosonic triplon excitations are shown host bands nontrivial higher-order topology. demonstrate this using real-space Bogoliubov--de Gennes calculations reveal existence near-mid band gap modes a signature bulk provide an understanding in systems via computation topological invariants well construction edge theories and study their phase transitions tune parameters model Hamiltonians. also discuss possible experimental approaches for detecting emergent modes.