Topological Surface States Penetrate Through Surface Barriers

Topological surface states are a new class of novel electronic states that are potentially useful for quantum computing or spintronicapplications. Unlike conventional two-dimensional electron states, these surface states are expected to be immune to localization and to overcome barriers caused by material imperfection. Previous experiments have demonstrated that topological surface states do not backscatter between equal and opposite momentum states, due to their chiralspin texture. However, to date, there is no evidence as to whether these states in fact transmit through natural occurring surface defects and consequently are connected on the exterior of a bulk sample regardless of its shape. We used a scanning tunneling microscope to measure transmission and reflection probability of Sb’s topological surface states through naturally occurring crystalline steps separating atomic terraces. In contrast to non-topological surface states of common metals (Cu, Ag, Au), which are either reflected or absorbed by atomic steps, we show topological surface states of Sbto penetrate through such barriers with high probability. This demonstration of the extended nature of Sb’stopological surface states suggests that such states may be useful for high current transmission even in the presence of atomic scale irregularities—an electronic feature sought to efficiently interconnect nanoscaledevices.

Building a Fabry-Perot Interferometer for topological surface states. Evidence for transmission of the surface state can be seen in flat terrace at specific energies  (arrows). Similar barriers fully reflect conventional surface state (Cu, Ag, Au). Experiments such as this demonstrate that in Sb the probability for transmission and reflection are about equal at 40%. In Sb the presence of a hole pocket makes it possible that there is a reflection, which is advantages as it allows both transmission & reflection to be measured using the STM.