Journal Article

Transmission of topological surface states through surface barriers

Seo, Jungpil, Cava, R. J., Hor, Y. S., Yazdani, Ali, Roushan, Pedram, Beidenkopf, Haim

2010

Overview

Breaking down barriers Topological states have become the subject of much attention from condensed-matter physicists, as evidence accumulates to show that these states can be found on the surface of certain materials — in particular, bulk compounds called topological insulators. As a product of their topological nature, topological surface states are predicted to have the remarkable property of being robust against imperfections. This can allow, for example, the conduction of electronic currents without dissipation. Ali Yazdani and his team now report a tantalizing finding from scanning tunnelling microscope measurements — that topological surface states on antimony can be transmitted with high probability through naturally occurring barriers that stop other conventional surface states of common metals. The authors suggest that their findings indicate that topological surface states could be exploited in novel applications of nanoscale electronic devices. Topological surface states are a class of electronic states that might be of interest in quantum computing or spintronic applications. They are predicted to be robust against imperfections, but so far there has been no evidence that these states do transmit through naturally occurring surface defects. Here, scanning tunnelling microscopy has been used to show that topological surface states of antimony can be transmitted through naturally occurring barriers that block non-topological surface states of common metals. Topological surface states are a class of novel electronic states that are of potential interest in quantum computing or spintronic applications 1 , 2 , 3 , 4 , 5 , 6 , 7 . Unlike conventional two-dimensional electron states, these surface states are expected to be immune to localization and to overcome barriers caused by material imperfection 8 , 9 , 10 , 11 , 12 , 13 , 14 . Previous experiments have demonstrated that topological surface states do not backscatter between equal and opposite momentum states, owing to their chiral spin texture 15 , 16 , 17 , 18 . However, so far there is no evidence that these states in fact transmit through naturally occurring surface defects. Here we use a scanning tunnelling microscope to measure the transmission and reflection probabilities of topological surface states of antimony through naturally occurring crystalline steps separating atomic terraces. In contrast to non-topological surface states of common metals (copper, silver and gold) 19 , 20 , 21 , 22 , 23 , which are either reflected or absorbed by atomic steps, we show that topological surface states of antimony penetrate such barriers with high probability. This demonstration of the extended nature of antimony’s topological 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 nanoscale devices.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/301/119/1000 / 639/766/25 / 639/925/927 / Antimony / Barriers / Bridgman method / Chemical properties / Condensed matter / Condensed matter: electronic structure, electrical, magnetic, and optical properties / Condensed matter: structure, mechanical and thermal properties / Crystal structure / Devices / Electron states / Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures / Electronics / Exact sciences and technology / Fourier transforms / Humanities and Social Sciences / letter / multidisciplinary / Nanostructure / Physics / Quantum computing / Sample size / Science / Science (multidisciplinary) / Silver / Solid surfaces and solid-solid interfaces / Surface and interface electron states / Surface layer / Surface states, band structure, electron density of states / Surface structure and topography / Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties) / Texture