Higher-order Topological States in Chiral Split Magnons of Honeycomb Altermagnets

Abstract: We theoretically explore higher-order topological magnons in collinear altermagnets, encompassing a dimensional hierarchy ranging from localized corner modes to propagating hinge excitations. By employing antiferromagnetic interlayer coupling in bosonic Bogoliubov-de Gennes (BdG) Hamiltonian, our work reveals anisotropic surface states and spatially distributed hinge modes within AA-type stacking configurations. We track the adiabatic evolution of Wannier centers to identify the bulk-polarization with second-order topological magnon insulator (SOTMI), where various magnon spectra demonstrate symmetry-protected band structure beyond conventional topology. Harnessing the stability and propagative properties of hinge modes, our study offers a potential platform for magnonic quantum information processing in altermagnetic systems that performs energy-efficient logic operation.