Doped nanowires of crystalline topological insulator near superconductivity threshold

In the theory-led field of topological materials—unusual states of matter with special symmetries that lock in distinct quantum properties—experimentalists are racing to the goal: fabrication methods that reliably yield topological insulators and superconductors, enabling a host of spintronic devices and even a robust quantum computer.

In APL Materials, Yale University scientists report making nanowires that reached the onset of superconductivity in tin-telluride, a known topological crystalline insulator with symmetry-protected surface states. Using a standard chemical vapor deposition process employing gold catalysts, the team synthesized indium-doped (4-6%) tin-telluride nanowires (up to 300 nanometers wide). The doped compound is known to superconduct at about 2 Kelvin.

Four probe measurements of the nano wire devices showed a significant drop in resistance below 1.75 K, signaling the transition to superconductivity. Although the collaborators, led by Piranavan Kumaravadivel and Judy Cha, did not observe resistance-free passage of current, additional tests confirmed “superconducting-like correlations,” the first such demonstration of this behavior in indium-doped tin-telluride nanowires, they report.

Follow-on tests also eliminated quantum phase slips as the cause of the gradual resistance drop detected in the nanowires.

In control experiments with larger structures—nanoribbons and even wider nanoplates—the team determined the occurrence of superconductivity. However, according to Cha, superconducting nanowires are the preferred route toward building quantum computers that exploit the robust properties and behavior of topological materials. Though the team achieved only partial success, Cha says the results underscore the importance of material quality in synthesizing fully superconducting nanowires, useful information for others in the field. In the current work, less than fully uniform dispersion of indium and, perhaps, clusters of gold particles are suspected impediments.

Source: “Synthesis and superconductivity of In-doped SnTe nanostructures,” by Piranavan Kumaravadivel, Grace A. Pan, Yu Zhou, Yujun Xie, Pengzi Liu, and Judy J. Cha, APL Materials (2017). The article can be accessed at https://doi.org/10.1063/1.4994293 .