Fig. 2: Geometry of a finite-size structure and corner charges.
From: Two-dimensional higher-order topology in monolayer graphdiyne
a A finite-size structure of MGD preserving P and My symmetries designed to observe the higher-order band topology protected by P symmetry. The red horizontal line indicates the My-invariant line. b Electron density distribution for a finite-size MGD composed of 9 × 9 unit cells where hydrogen atoms are attached at every corner except at the two My-invariant corners. To resolve the filling anomaly, we add one electron to MGD additionally and fill the valence band completely. The accumulated or depleted charges with respect to the half-filled configuration are plotted. Here, a half-integral charge accumulated at each My-invariant corner appears due to the nontrivial 2D topological invariant w2 = 1.
