Scattering from Monolayer and Bilayer Step Edges on Topological Sb(111)*

The topological semimetal antimony (Sb) has a layered structure that cleaves easily along the 111 plane,
typically exposing large, atomically flat terraces separated by bilayer steps. Reflection and transmission
of 2D surface states from these step edges can be used to quantify the topological protection against
backscattering. Here we use scanning tunneling microscopy (STM) to image the cleaved surface of
Sb(111). In addition to the expected bilayer steps, we occasionally find monolayer steps, as well as a
combination of mesa, stair, and valley terraces. We use spectroscopic STM to probe the quantized
energy levels of surface states on each of these terraces, and compare to the energy quantization that
would be expected from the visible terrace width. Our analysis indicates that surface states are more
easily transmitted under adjacent terraces, i.e. there is less backscattering from upward step edges.