Second-order topological insulator induced by compensated altermagnetism without bulk spin splitting
arXiv:2607.12323 · doi:10.1103/7q2z-317r
The paper theoretically shows that a two‑dimensional topological insulator film can host a second‑order topological insulating phase when a compensated altermagnetic term is added, preserving bulk spin degeneracy while gapping edge states and creating localized corner states.
Abstract
We theoretically demonstrate a second-order topological insulating phase induced by compensated altermagnetism, while keeping the bulk gap unchanged, in a two-dimensional topological insulator film. By introducing a layer-resolved out-of-plane -wave altermagnetic term with opposite signs on the top and bottom layers, the system preserves symmetry and maintains spin degeneracy in the bulk bands, while simultaneously gapping the helical edge states and generating localized corner states. The resulting higher-order phase is characterized by nonzero mirror-graded winding numbers, and an effective edge theory shows that the corner states arise from Dirac mass domain walls. We further determine the phase boundaries analytically and construct the corresponding topological phase diagram, establishing a robust route to higher-order topology without bulk spin splitting.