Fast and fragile: Two new studies explain the strange electron flow in future materials

Amazing stuff! 

"For the past 15 years, a class of materials known as topological insulators has dominated the search for the materials of the future. ... Such materials could enable technologies that perform faster and are more energy-efficient than today's devices.

That was the picture until the discovery two years ago that some topological materials are actually unable to conduct current on their surface, a phenomenon that earned the name "fragile topology."

"Fragile topology is a strange beast: It is now predicted to exist in hundreds of materials," ... To get a handle on how fragile states form, the researchers turned to two resources: mathematical equations and 3D printers. ... tested the theory by building a life-sized topological material out of 3D-printed plastics ... the roughly 20,000 or so topological materials identified to date. The theoretical underpinnings of topological materials earned a 2016 Nobel Prize in Physics ... This principle of "bulk-boundary correspondence" to explain topological surface conduction was widely accepted until two years ago, when a handful of scientific papers revealed the existence of fragile topology. Unlike the usual topological states, fragile topological states do not have conducting surface states.
"The usual bulk-boundary correspondence principle breaks down," ... But exactly how remained a puzzle. ..."

Fast and fragile: Two new studies explain the strange electron flow in future materials | Office of the Dean for Research: For the past 15 years, a class of materials known as topological insulators has dominated the search for the materials of the future. These crystals have an uncommon property: Their interiors are insulators — where electrons cannot flow — but their surfaces are perfect conductors, where electrons flow without resistance. Such materials could enable technologies that perform faster and are more energy-efficient than today's devices.

That was the picture until the discovery two years ago that some topological materials are actually unable to conduct current on their surface, a phenomenon that earned the name "fragile topology."

"Fragile topology is a strange beast: It is now predicted to exist in hundreds of materials,"