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.”

Read the full story in the Cornell Chronicle.

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.

How to train a magnet: Excitons as a new knob for magnetic control

Scientists can learn a lot about a quantum material by watching how it responds to light. In magnetic semiconductors, one especially useful messenger is the exciton: a pairing of a negatively charged electron and the positively charged “hole” it leaves behind.

Until now, excitons in magnetic materials have mostly been used as reporters. They could reveal how spins were arranged or how magnetic waves moved through a material. But Cornell researchers have shown that excitons can do more than observe magnetism. They can actively steer it.

In “Excitonic Spin Torque in a Magnetic Semiconductor,” published June 15 in Nature Materials, Youn Jue (Eunice) Bae, assistant professor of chemistry and chemical biology in the College of Arts and Sciences, and colleagues report that excitons created by light can exert a spin torque in the two-dimensional magnetic semiconductor chromium sulfide bromide, or CrSBr. The finding establishes excitons as a new way to control magnetic motion with light.

Read the full story in the Cornell College of Arts & Sciences website.