An illustration of topological surface states in bismuth iodide as seen by angle-resolved photoemission spectroscopy. Credit: Oleg Yazyev (EPFL)
Topological insulators are materials that let electric current flow across their surface while keeping it from passing it through their bulk. This exotic property makes topological insulators very promising for electricity with less energy loss, spintronics, and perhaps even quantum computing. EPFL scientists have now identified a new class of topological insulators, and have discovered its first representative material, which could propel topological insulators into applications.
By theoretically testing potential candidates from the database of previously described materials, Oleg Yazyev EPFL team has identified a material, “crystalline phase” of bismuth iodide, as the first of a new class of topological insulators. What makes this material particularly exciting is that its atomic structure does not resemble any other topological insulator known to date, which makes its properties very different as well.
One clear advantage of bismuth iodide is that its structure is more ordered than that of previously known topological insulators, and with fewer natural defects. In order to have an insulating interior, a material must have as few defects in its structure as possible.
After characterizing bismuth iodide with theoretical tools, the scientists tested it experimentally with an array of methods. The main evidence came from a direct experimental technique called “angle-resolved photoemission spectroscopy”. This method allows researchers to “see” electronic states on the surface of a solid material, and has become a key technique for proving the topological nature of electronic states at the surface.
The measurements, carried out at the Lawrence Berkeley National Lab, proved to be fully consistent with the theoretical predictions made by Gabriel Autès. The actual electron structure calculations were performed at the Swiss National Supercomputing Centre, while data analysis included a number of scientists from EPFL and other institutions.
The lab is now exploring further the properties of bismuth iodide, as well materials with similar structures. Meanwhile, other labs are joining the effort to support the theory behind the new class of topological insulators and propagate the experimental efforts.
http://phys.org/news/2015-12-spintronics-low-energy-electricity-closer-class.htmljCp
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