Buckled honeycomb group-$V$--$S_6$ symmetric $(d-2)$ higher order topological insulators

Higher Order Topological Insulators (HOTI) are $d$-spatial dimensional systems featuring topologically protected gap-less states at their $(d-n)$-dimensional boundaries. With the help of $\mathit{\text{ab-initio}}$ calculations and tight binding models along with symmetry considerations we show that monolayer buckled honeycomb structures of group-V elements (Sb,As), which have already been synthesized, belong in this category and have a charge fractionalization of $\frac{e}{2}$ at the corner states as well as weak topological edge states, all protected by their properties under the inversion operation which classify this system as a quadrupole topological insulator.