Towards topological quasifreestanding stanene via substrate engineering

In search for a new generation of spintronics hardware, material candidates for room temperature quantum spin Hall effect (QSHE) have become a contemporary focus of investigation. Inspired by the original proposal for QSHE in graphene, several heterostructures have been synthesized, aiming at a hexagonal monolayer of heavier group IV elements promoting the QSHE bulk gap via increased spin-orbit coupling. So far, the monolayer/substrate coupling, which can manifest itself in strain, deformation, and hybridization, has proven to be detrimental to the aspired QSHE conditions for the monolayer. For stanene, the Sn analog of graphene, we investigate how an interposing buffer layer mediates between monolayer and substrate in order to optimize the QSHE setting. From a detailed density functional theory study, we highlight the principal mechanisms induced by such a buffer layer to accomplish quasifreestanding stanene in its QSHE phase. We complement our theoretical predictions by presenting attempts to grow a buffer layer on SiC(0001) on which stanene can be deposited.