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| Purdue University's Yang Xu inspects devices made from topological insulators under a microscope before electrical measurements are made on the samples. (Courtesy: Purdue University/Ting-fung Chung) |
Researchers in the US say that they have made the best 3D topological insulator to date. The material is called bismuth antimony tellurium selenide (BiSbTeSe2) and could be of fundamental importance for testing a number of condensed-matter and particle-physics theories. The material could also find use in spintronics devices and be used to build robust topological quantum bits (qubits) for quantum computers.
Topological insulators are materials that are electrical insulators in the bulk but can conduct electricity on their surface via special surface electronic states. "Most topological insulators made to date have not been completely insulating in the bulk, because of impurities (unintentionally introduced during material synthesis or processing) that doped the bulk and made it conducting," explains Yong Chen of Purdue University, who led the research. "Our topological insulator appears not to conduct at all in the bulk but does so only at its surface."
The researchers worked this out by measuring how thin flakes of BiSbTeSe2 of various thicknesses conducted electricity. They found that the conductance of different samples was almost independent of their thicknesses. Such behaviour is completely different to that seen in normal 3D materials, in which conductance is proportional to sample thickness.
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