Activation of topological insulator phase in kagomé-type bilayers by interlayer coupling: The cases of Ni(CO)4 and Pd(CO)4

We predict that a 2D kagomé-type topological insulator (TI) can be built as a bilayer of a single-layer material that is not a TI. We demonstrate this through first-principles calculations of a class of C 6 O 6 and C 6 ( NH ) 6 based 2D metal-organic frameworks. We find that minimum-energy bilayers of two compounds of this class, with stoichiometries Ni ( CO ) 4 and Pd ( CO ) 4, are intrinsic topological insulators although their isolated single-layer components are trivial metals. The first-principles results for the single-layer and bilayer systems are reproduced by tight-binding models. The simplicity of the models suggests that other bilayer TI systems of this type should exist, not necessarily composed of metal-organic frameworks, as long as they are composed of kagomé-type systems in a AA stacking.