Perfect Transmission of Topological Surface States Through Monolayer Step Edges on Sb(111)

Topological surface states are unconventional two-dimensional electronic states that have chiral spin texture and are protected from backscattering. Previous experiments show that topological surface states have an enhanced transmission and a reduced reflection at the common bilayer step edges on the (111) surface of topological semimetal antimony (Sb). Using scanning tunneling microscopy and spectroscopy, we study successive monolayer step edges as partial dislocations on the (111) surface of Sb. We demonstrate from the quasiparticle interference pattern that the topological surface states are backscattered within two adjacent monolayer steps as a whole bilayer step. Remarkably, we find that the topological surface states transmit perfectly through the transitional monolayer step edge.