Two-atom-thin topological crystalline insulators lacking out of plane inversion symmetry
arXiv:2211.05245 · doi:10.1088/1361-648X/aca135
Abstract
A two-dimensional topological crystalline insulator (TCI) with a single unit cell (u.c.) thickness is demonstrated here. To that end, one first shows that tetragonal ( in-plane) symmetry is not a necessary condition for the creation of zero-energy metallic surface states on TCI slabs of finite-thicknesses, because zero-energy states persist even as all the in-plane rotational symmetries--furnishing topological protection--are completely removed. In other words, zero-energy levels on the model are not due to (nor are they protected by) topology. Furthermore, effective twofold energy degeneracies taking place at few discrete points away from zero energy in the bulk Hamiltonian--that are topologically protected--persist at the u.c.~thickness limit. The chiral nature of the bulk TCI Hamiltonian permits creating a square Hamiltonian, whose topological properties remarkably hold invariant at both the bulk and at the single u.c.~thickness limits. The identical topological characterization for bulk and u.c.-thick phases is further guaranteed by a calculation involving Pfaffians. This way, a two-atom-thick TCI is deployed hereby, in a demonstration of a topological phase that holds both in the bulk, and in two dimensions.
arXiv comment14 pages, 8 figures, accepted at Journal of Physics: Condensed Matter on 11/7/2022
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