Schematic of a higher-order topological insulator in the shape of a nanowire. Note conducting channels on its edges. Source: UZH

The field of topology examines properties of objects and solids that are preserved under continuous deformation. One such material is known as a topological insulator — a crystal that insulates on the inside, while conducting electrical current on their surfaces.

Now, theoretical physicists at the University of Zurich (UZH) have predicted a new class of such insulators; these crystals have conducting properties on their edges, rather than on their surface. The research team dubbed the new material class "higher-order topological insulators," and what makes them particularly interesting is their extraordinary robustness. The current cannot be stopped by disorder or impurity; if an imperfection gets in the way, the current simply flows around it. And if the crystal breaks, the new edges also conduct current, automatically.

“The most exciting aspect is that electricity can at least in theory be conducted without any dissipation," said Titus Neupert, a UZH physics professor. "You could think of the crystal edges as a kind of highway for electrons. They can't simply make a U-turn."

This property, known as dissipationless conductance, is not shared with previously known topological insulator crystals with conducting surfaces. It is, however, observed in superconductors at low temperatures.

At present, the study relies mostly on theory. Tin telluride is one compound the researchers believe will show these novel properties; Neupert acknowledges that more material candidates need to be identified and probed through experiments. In the future, however, nanowires made of higher-order topological insulators could be used as conducting paths in electric circuits — and combined with magnetic and superconducting materials, and used in the building of quantum computers.