Prediction of intrinsic two-dimensional non-Dirac topological insulators in triangular metal-organic frameworks

Two-dimensional (2D) metal-organic frameworks (MOFs) with topologically nontrivial states have attracted considerable attention recently. Based on ab initio calculations, we demonstrate that Cu(C21N3H15) with a triangular lattice is an intrinsic quantum anomalous Hall insulator. The multiple p (px and py)-like molecular orbitals of the C21N3H15 molecule with C3 symmetry give rise to a degenerate energy point at the Γ point with quadratic non-Dirac band dispersions. When the spin-orbit coupling is included, the bandgap is opened around the non-Dirac Γ point and a topologically nontrivial state is achieved. Quantum spin Hall effects can also be realized in this kind of 2D triangular lattice MOF if the time-reversal symmetry is preserved, as proposed in the Ni(C21N3H15) lattice. The physical mechanism is analyzed through a k · p model built. Our results present that the 2D triangular lattice MOFs are excellent candidates for producing 2D topological insulators and might have promising applications in future microelectronics and spintronics.