researchers at the university of pennsylvania, along with scientists at johns hopkins university and goucher college, have discovered new topological insulators, which only carry current along the surface of the material, with superconducting properties that could be used to create fault-tolerant quantum computers.
a false color image of one of the researchers' samples. (university of pennsylvania)
an article on the university of pennsylvania website explained that this discovery was made during research into the making of devices out of topological insulators.
during the work, one of the devices blew up as it would have in a short circuit. the researchers measured the resistance of the melted region and found that it had become superconducting. an examination of the materials present showed only bismuth selenide and palladium.
the article added, “when superconducting materials are cooled, they can carry a current with zero electrical resistance without losing any energy…however, it is difficult to make good electrical contact between the topological insulator and superconductor and to scale such devices for manufacture, using current techniques. if this new material could be recreated, it could potentially overcome both of these difficulties.”
to recreate the conditions of the material after its short circuit, the researchers heated it in a furnace to a certain temperature that allowed the metal to directly enter the nanostructure. this provided the necessary electrical contact and, with standard lithography, the researchers demonstrated that the metal could be patterned as desired.
“by patterning it directly into the crystal, the superconductor is embedded, and there are none of these contact problems,” the article noted. “the resistance is very low, and they can pattern devices for quantum computing in one single crystal.”
the material was tested in extreme cold, as low as near absolute zero. magnetic fields were also passed over it to test its limitations and standard voltage tests were conducted.
“one of the benefits of the researchers’ device is that it's potentially scalable, capable of fitting onto a chip similar to the ones currently in our computers,” the article added.
the research was recently published in acs nano. the abstract read:
“topologically protected states in combination with superconductivity hold great promise for quantum computing applications, but the progress on electrical transport measurements in such systems has been impeded by the difficulty of fabricating devices with reliable electrical contacts.
“we find that superconductivity can be patterned directly into bi2se3 nanostructures by local doping with palladium. superconducting regions are defined by depositing palladium on top of the nanostructures using electron beam lithography followed by in situ annealing.
“electrical transport measurements at low temperatures show either partial or full superconducting transition, depending on the doping conditions.
“structural characterization techniques indicate that palladium remains localized in the targeted areas, making it possible to pattern superconducting circuits of arbitrary shapes in this topological material.”