Topological materials: not as exotic as we thought

Solids, liquids, gases, plasma: phases – or states – of materials. Thouless, Haldane and Kosterlitz won the Nobel Prize for Physics in 2016 for their discovery of the less well-known topological phases. These new material states behave in a surprising way: topological insulators are electrical insulators in their bulk, whereas an electric current can propagate without resistance on their surface. Until now seen as curiosities of nature, an international team including a CNRS researcher1 has demonstrated that these properties are in fact much more widespread than expected. They affect more than a quarter of natural inorganic materials. From a theory called “topological quantum chemistry,” which predicts the topological properties of materials from how their atoms are arranged, the researchers have developed a number of digital codes that can be used to classify inorganic materials present in a reference database2 . Of 26,938 materials studied3 , 12 % were shown to be topological insulators, and 15 % semi-metals (semi-metals are the other large class of topological materials, intermediate between insulators and metals). The researches now want to predict new topological materials using artificial intelligence and their database. This discovery bodes well for a bright future for these materials, which we can tell will play a role in quantum computing.

• 1Nicolas Regnault, CNRS researcher at the ENS Laboratoire de Physique (CNRS/ENS/Sorbonne Université/Université Paris Diderot), with colleagues at University of the Basque Country (Spain), Max Planck Institute for Chemical Physics of Solids (Germany), Princeton University (USA).
• 2Inorganic Crystal Structure Database: this database contains the fine structure (atom positions) of all known inorganic materials, obtained by crystallography.
• 3Materials called “high quality” in the database.