Researchers at the University of Chicago’s Pritzker School of Molecular Engineering and collaborators used layer-by-layer growth of bismuth telluride films to make ordered two-dimensional topological-insulator structures on a millimeter scale. The university’s October 12 release discusses an ACS Nano paper published online on October 9. The study examined two-quintuple-layer Bi₂Te₃ and MnBi₂Te₄/Bi₂Te₃ heterostructures; the films grew in a coherent, carpet-like form across the sample.

The team used angle- and photon-energy-dependent photoemission to study how the electronic band structure changes with layer count, and time-resolved photoemission to examine electron dynamics. Collaborators at Northwestern University used scanning tunneling spectroscopy to measure signals at the film edges consistent with conducting edge states. The researchers also reported that changing the top layer to manganese bismuth telluride widened the band gap. The university release says electrical-resistance measurements have not yet been made and are a next validation step. The work therefore reports spectroscopic evidence, not measured device performance or mass production. The paper’s first page lists US affiliations at the universities of Chicago, Northwestern, Illinois Urbana-Champaign, Florida and Penn State.