IMX Seminar Series - Atomic monolayers as two-dimensional topological insulators

Two-dimensional topological insulators (2D-TIs) are characterized by hosting spin-polarized conducting band states at their one-dimensional (1D) edges, giving rise to the quantum spin Hall (QSH) effect. As pointed out in the seminal work of Kane and Mele, graphene would constitute the most simple realization of a QSH insulator if it were not for its almost negligible spin-orbit interaction. It has been suggested that going to heavier group IV monolayers (such as the Sn-derived "stanene") could remedy this problem, but a convincing demonstration of such 2D TIs is still lacking. Recently it has been found that going to the neighboring groups III and V in the Periodic Table provides a promising alternative approach. Here I will discuss our recent photoemission (ARPES) and scanning tunneling microscopy (STM) studies of such monolayer systems. Particular focus will be on the case of bismuthene deposited on a SiC(0001) substrate, which is identified as a large band-gap QSH insulator with almost atomically confined 1D edge states. Time permitting I will also address our recent discovery of possible topological behavior in triangular In monolayers on SiC.