A new ingredient for quantum computing: krypton gas

To commercialize quantum computing, manufacturers need high-quality superconducting materials for microchips, but they also require a reliable, sustainable nanofabrication process.

Tantalum is a corrosion-resistant metal that meets the first criteria but not the second. That’s because it has to be deposited on a substrate at temperatures that typically exceed 400 degrees Celsius – too hot for many semiconductor foundries’ current tools.

Cornell researchers have developed a method that uses krypton gas to slash that deposition temperature to 200 degrees while depositing on silicon, a standard high-quality substrate. The process resulted in thin films that also have substantially higher electronic conductivity.

“Tantalum as a material has been shown to be very exciting from a device performance perspective, but its manufacturability had some question marks because of integration challenges such as required process temperatures,” said Valla Fatemi, assistant professor and Aref and Manon Lahham Faculty Fellow in the Cornell Duffield College of Engineering, who led the project.

Read the full story in the Cornell Chronicle.

Researchers break light symmetry with simple materials

Light typically interacts with a material the same way whether it enters through the front or the back – like polarized sunglasses that work the same from either side. Cornell researchers have demonstrated a simple route to breaking that symmetry, opening new possibilities for photonics and quantum information processing.

Optical reciprocity, the principle that a system responds identically regardless of which side faces the light, underlies most lenses, mirrors and other optical devices. A new study published July 27 in Nature Materials demonstrates that some materials can be engineered to exhibit nonreciprocal absorption and emission of linearly polarized light.

“Imagine window blinds with sunlight coming through its horizontal slats, but from the opposite side, the same blinds let light through as if the slats were vertical, completely inverted,” said corresponding author Richard Robinson, professor of materials science and engineering in the Cornell Duffield College of Engineering. “To get this type of behavior, you typically need complex metamaterials or external magnetic fields, but we show that it can be achieved in simple, solution-processed semiconductor nanoclusters.”

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Too thin to fail: an alternative to copper microchip interconnects

Electrical interconnects may very well be the unsung heroes of modern microchips.

These tiny wires – typically made of copper due to its high conductivity – string together the billions of transistors that drive our computers and electronic devices. But as the technology advances and additional transistors are piled on, the components must shrink to the nanoscale. And that’s when copper begins to fail.

Cornell researchers have developed a potential replacement for copper interconnects: single-crystal nanowires of niobium arsenide. This topological semimetal paradoxically becomes a better conductor the thinner it gets, boosting electronic performance.

The findings were reported July 16 in Science. The lead author is doctoral student Yeryun Cheon. Judy Cha, the Rick and Betty Tsai Ph.D. 1981 Professor in Materials Science and Engineering in the Cornell Duffield College of Engineering, is the paper’s senior author.

Read the full story in the Cornell Chronicle.