AsianScientist (Aug. 6, 2014) – Scientists have shown that samarium hexaboride (SmB6) can act as a topological insulator, making it a suitable material for the emerging field of spintronics. This research has been published in the journal Nature Communications.
In spintronics, devices work by manipulating the spin of electrons rather than the current generated by their motion. Spin can take either of two possible states: “up” or “down”, which can be pictured respectively as clockwise or counter-clockwise rotation of the electron around its axis. Controlling electron spin can be achieved with materials called ‘topological insulators’, which conduct electrons only across their surface but not through their interior.
However, topological insulators are still in the experimental phase. One particular insulator, SmB6, has been of great interest. Unlike other topological insulators, SmB6‘s insulating properties are based on a special phenomenon called the ‘Kondo effect’. The Kondo effect prevents the flow of electrons from being destroyed by irregularities in the material’s structure, making SmB6 a very robust and efficient topological ‘Kondo’ insulator.
Scientists from the Paul Scherrer Institute (PSI), the Institute of Physics at the Chinese Academy of Sciences and École Polytechnique Fédérale de Lausanne (EPFL) have now shown experimentally that SmB6 is the first topological Kondo insulator.
In experiments carried out at the PSI, the researchers illuminated samples of SmB6 with a special type of light called synchroton radiation. The energy of this light was transferred to electrons in SmB6, causing them to be ejected from it. The properties of ejected electrons, including spin, were measured with a detector, which gave clues about how the electrons behaved while they were still on the surface of SmB6. The data showed consistent agreement with the predictions for a topological insulator.
“The only real verification that SmB6 is a topological Kondo insulator comes from directly measuring the electron spin and how it’s affected in a Kondo insulator”, says Professor Hugo Dil from EPFL.
Although SmB6 shows insulating behavior only at very low temperatures the experiments provide a proof of principle, and more importantly, that Kondo topological insulators actually exist, offering an exciting stepping-stone into a new era of technology.
The article can be found at: Xu et al. (2014) Direct Observation of the Spin Texture in SmB6 as Evidence of the Topological Kondo Insulator.
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Source: École Polytechnique Fédérale de Lausanne; Photo: SLAC National Accelerator Laboratory/Flickr/CC.
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