  We propose a new correlated topological state which we call a higher-order
topological Mott insulator (HOTMI). This state exhibits a striking
bulk-boundary correspondence due to electron correlations. Namely, the
topological properties in the bulk, characterized by the Z3 spin-Berry phase,
result in gapless corner modes emerging only in spin excitations (i.e., the
single-particle excitations remain gapped around the corner). We demonstrate
the emergence of the HOTMI in a Hubbard model on the kagome lattice, and
elucidate how strong correlations change gapless corner modes at the
noninteracting case.
