Two dimensional honeycomb-kagome Be 3 Pb 2 : a mechanically flexible topological insulator with high intrinsic carrier mobilities.

We theoretically predict a stable 2D nanosheet consisting of Pb and Be atoms sited at the honeycomb and kagome sites, respectively, forming a mixed honeycomb-kagome phase of Be3Pb2. Without the spin-orbit interaction, its band structure resembles that of honeycomb-structured graphene, namely, the valence and conduction bands touch at isolated points, whose energies linearly depend on the momentum. The presence of spin-orbit coupling (SOC), however, would result in a small bandgap opening, ∼116 meV. So, the SOC induces an electronic phase transition from a semimetal to a semiconductor. A coarse estimation based on the deformation potential method gives rise to very high carrier mobilities which are at least comparable to those of black phosphorene. Most interestingly, the 2D Be3Pb2 shows a non-trivial topology in the electronic structure accompanying the SOC induced band gap opening. Hence, 2D Be3Pb2 would be a versatile candidate for many applications, e.g., nanoelectronic devices.