Topological properties of buckled 2D hoyneycomb group-V elements

The honeycomb form of 2D group V-elements (Sb,As) was recently shown to undergo distinct topological phase transitions as function of buckling.[1] Starting out as a nodal line semimetal in the flat form, Dirac points emerge when slight buckling is introduced, which annihilate in pairs upon further buckling. Here we show that the buckled lowest energy form at the end of this series of topological transitions is a weak topological crystalline insulator (TCI) in the obstructed atomic limit (OAL).[2] Relations to the kagome, Kekul\'e and Su-Schrieffer-Heeger systems are pointed out. Further group theoretical analysis, shows that this system is a (d-2) higher order topological insulator. The resulting corner states are shown to be robust as long as the disorder remains restricted to the bulk rather than the edges. The edge states and corner states at zero energy can be gapped by breaking the inversion symmetry, which we show to lead to the possibility of a topological quantized conductance metal insulator transition by application of an electrical field perpendicular to the layers. Finally, we note that the formation of an OAL is a universal property of the annihilation of Dirac fermions of opposite winding.
[1] SKR WRL, PRB 101, 235111 (2020)
[2] SKR WRL, PRB 102, 115104 (2020)