Subnanometre-wide electron channels protected by topology

Helical locking of spin and momentum and prohibited backscattering are the key properties of topologically protected states(1,2). They are expected to enable novel types of information processing by providing pure spin currents(3,4), or fault tolerant quantum computation by using the Majorana fermions at interfaces of topological states with superconductors(5). So far, the required helical conduction channels used to realize Majorana fermions are generated through the application of an axial magnetic field to conventional semiconductor nanowires(6). Avoiding the magnetic field enhances the possibilities for circuit design significantly(7). Here, we show that subnanometre-wide electron channels with natural helicity are present at surface step edges of the weak topological insulator Bi14Rh3I9 (ref. 8). Scanning tunneling spectroscopy reveals the electron channels to be continuous in both energy and space within a large bandgap of 200 meV, evidencing its non-trivial topology. The absence of these channels in the closely related, but topologically trivial compound Bi13Pt3I7 corroborates the channels' topological nature. The backscatter-free electron channels are a direct consequence of Bi14Rh3I9's structure: a stack of two-dimensional topologically insulating, graphene-like planes separated by trivial insulators. We demonstrate that the surface of Bi14Rh3I9 can be engraved using an atomic force microscope, allowing networks of protected channels to be patterned with nanometre precision.