Two-atom-thin topological crystalline insulators lacking out of plane inversion symmetry

A two-dimensional topological crystalline insulator (TCI) with a single unit cell (u.c.) thickness is demonstrated here. The chiral nature of the bulk TCI Hamiltonian from Fu [1] permits creating a 2x2 square Hamiltonian, whose topological properties 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.

[1]. L. Fu. Phys. Rev. Lett. 106, 106802 (2011).