Sub-nm wide electron channels protected by topology

TL;DR

This paper reports the discovery of sub-nanometer wide, topologically protected electron channels at surface step-edges of Bi14Rh3I9, which are continuous, non-trivial, and can be patterned with atomic precision, advancing topological electronics.

Contribution

It demonstrates the existence of natural, protected helical electron channels in a topological insulator without magnetic fields and shows they can be precisely patterned using atomic force microscopy.

Findings

Electron channels are continuous within a 200 meV band gap.

Channels are absent in a topologically trivial insulator.

Surface patterning of protected channels is achievable with atomic force microscopy.

Abstract

Helical locking of spin and momentum and prohibited backscattering are the key properties of topologically protected states. They are expected to enable novel types of information processing such as spintronics by providing pure spin currents, or fault tolerant quantum computation by using the Majorana fermions at interfaces of topological states with superconductors. So far, the required helical conduction channels used to realize Majorana fermions are generated through application of an axial magnetic field to conventional semiconductor nanowires. Avoiding the magnetic field enhances the possibilities for circuit design significantly. Here, we show that sub-nanometer wide electron channels with natural helicity are present at surface step-edges of the recently discovered topological insulator Bi14Rh3I9. Scanning tunneling spectroscopy reveals the electron channels to be continuous in both energy and space within a large band gap of 200 meV, thereby, evidencing its non-trivial topology. The absence of these channels in the closely related, but topologically trivial insulator Bi13Pt3I7 corroborates the channels' topological nature. The backscatter-free electron channels are a direct consequence of Bi14Rh3I9's structure, a stack of 2D 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 nm precision.