Multiorbital edge and corner states in black phosphorene

We theoretically study emergent edge/corner localized states in monolayer black phosphorene. Using the tight-binding model based on density functional theory, we find that multi-orbital band structure due to non-planar puckered geometry plays an essential role formation of boundary modes. In particular, demonstrate edge emerge at a along arbitrary crystallographic direction, and it can be understood from fact Wannier orbitals associated with $3p_x$, $3p_y$, $3p_z$ occupy all bond centers At corner where two edges intersect, show multiple corner-localized appear hybridization higher-order topological state nearby. These characteristic properties intuitively explained by simple topologically-equivalent angles are deformed $90^{\circ}$.