Correlated bulk-boundary correspondence of the higher-order topological insulator

In this talk, we propose a novel topological state which we call “higher-order topological Mott insulator” (HOTMI) [1]. It gives a distinct bulk-boundary correspondence from a conventional higher-order topological insulator; d-dimensional bulk topology of the HOTMI predicts the emergence of gapless states not in charge excitations but in spin excitations around (d−n)-dimensional boundaries with n = 2, ..., d. We numerically demonstrate that the Hubbard model on the kagome lattice gives the 2nd-order HOTMI states for d = 2. Specifically, the corner-Mott states appearing in the system under the open boundary condition, which is gapless only in the spin excitations, are predicted by the Z₃ spin Berry phase calculated in the bulk system.
[1] K. Kudo, T. Yoshida, and Y. Hatsugai, arXiv:1905.03484, (to appear in Phys. Rev. Lett.)