New database reveals that topological materials are quite common

In a major step forward for an area of research that earned the 2016 Nobel Prize in Physics, an international team has found that substances with exotic electronic behaviors called topological materials are in fact quite common, and include everyday elements such as arsenic and gold. The team created an online catalog to make it easy to design new topological materials using elements from the periodic table.

Topological materials have unexpected and strange properties that have shifted scientists' understanding of how electrons behave. Researchers hope these substances could form the basis for technologies of the future, such as low-power devices and quantum computing.

"Once the analysis was done and all the errors corrected, the result was astonishing: more than a quarter of all materials exhibit some sort of topology," said Andrei Bernevig, professor of physics at Princeton University and a senior author of a paper on this work in Nature. "Topology is ubiquitous in materials, not esoteric."

Topological materials are intriguing because their surfaces can conduct electricity without resistance, so they are potentially faster and more energy-efficient than today's technologies. Their name comes from an underlying theory that draws on topology, a branch of mathematics that describes objects by their ability to be stretched or bent.

The beginnings of the theoretical understanding of these states of matter formed the basis of the 2016 Nobel Prize in Physics, shared among Princeton University physics professor Duncan Haldane, Michael Kosterlitz of Brown University and David Thouless of the University of Washington, Seattle.

Until now, only a few hundred of the more than 200,000 known inorganic crystalline materials have been characterized as topological, and they were thought to be anomalies.

"When fully completed, this catalog will usher in a new era of topological material design," Bernevig said. "This is the beginning of a new type of periodic table where compounds and elements are indexed by their topological properties rather than by more traditional means." The international team included researchers from the US, Spain, France and Germany.

The team investigated about 25,000 inorganic materials whose atomic structures are experimentally known with precision and classified in the Inorganic Crystal Structure Database. Their results show that, rather than being rare, more than 27% of materials in nature are topological.

The newly created database allows visitors to select elements from the periodic table to create compounds that the user can then explore for their topological properties. More materials are currently being analyzed and placed in the database for future publication.

Two factors allowed the team to achieve the complex task of topologically classifying the 25,000 compounds. First, two years ago, some of the present authors developed a theory known as topological quantum chemistry and also reported in a paper in Nature. This theory is able to classify the topological properties of any material from the simple knowledge of the positions and nature of its atoms.

Second, in the current study, the team applied this theory to the compounds in the Inorganic Crystal Structure Database. In doing so, the researchers needed to devise, write and modify a large number of computerized instructions to calculate the energies of electrons in the materials.

"We had to go into these old programs and add new modules that would compute the required electronic properties," said Zhijun Wang, who was a postdoctoral research associate at Princeton and is now a professor at the Beijing National Laboratory for Condensed Matter Physics in China and the Institute of Physics, Chinese Academy of Sciences.

"We then needed to analyze these results and compute their topological properties based on our newly developed topological quantum chemistry methodology," explained Luis Elcoro, a professor at the University of the Basque Country in Bilbao, Spain.

The researchers wrote several sets of codes to obtain and analyze the topology of electrons in real materials, and have now made these codes available to the public through the Bilbao Crystallographic Server. With the help of the Max Planck Supercomputer Center in Garching, Germany, the researchers then ran their codes on the 25,000 compounds.

"Computationally, it was pretty incredibly intensive stuff," said Nicolas Regnault, a professor at Ecole Normale Superieure in Paris, France, and a research director at the French National Center for Scientific Research. "Fortunately, the theory showed us that we need to compute only a fraction of the data that we needed previously. We need to look at what the electron 'does' only in part of the parameter space to obtain the topology of the system."

"Our understanding of materials got much richer because of this classification," said Maia Garcia Vergniory, a researcher at Donostia International Physics Center in San Sebastian, Spain. "It is really the last line of understanding of properties of materials."

Claudia Felser, a professor at the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany, had earlier predicted that even gold is topological. "A lot of the material properties that we know – such as the color of gold – can be understood through topological reasoning," Felser said.

The team is now working to classify the topological nature of additional compounds in the database. The next steps involve identifying the compounds with the best versatility, conductivity and other properties, and experimentally verifying their topological nature. "One can then dream about a full topological periodic table," Bernevig said.

This story is adapted from material from Princeton University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.