Electrons race along the surface of certain unusual crystalline materials, except that sometimes they don't. Two new studies from Princeton researchers and their collaborators explain the source of the surprising behavior and chart a course for restoring conductivity in these remarkable crystals, prized for their potential use in future technologies including quantum computers.


The studies were published in the journal Science.


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.


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."

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