In a development that sounds like a physics party trick but is actually a fundamental breakthrough, researchers at the UCLA Samueli School of Engineering have shown that heat can be channeled through solid materials in concentrated, ray-shaped paths at room temperature - a phenomenon previously only observed at cryogenic temperatures, where things behave nicely and don't cause so much trouble.

Published in Nature Physics, the study led by Yongjie Hu, a professor of mechanical and aerospace engineering, observed this so-called phonon focusing in boron arsenide, a crystalline semiconductor that apparently has better thermal manners than most. Phonons - the atomic vibrations that carry heat and exhibit quantum behavior - typically scatter every which way at room temperature, spreading heat evenly like a polite but inefficient host. But in boron arsenide, they travel in coherent, wave-based paths, following routes dictated by the crystal structure, much like light through an optical fiber. This means engineers could potentially direct heat along planned nanoscale routes instead of waiting for it to spread and then trying to scrub it off with fans and heat sinks.

The team developed a nanoscale temperature mapping technique and observed that while conventional materials spread heat in boring circular patterns, boron arsenide produced distinct ray-shaped patterns aligned with specific crystal directions. The patterns shifted predictably with crystal orientation, yielding sixfold, eightfold, and fourfold focusing patterns depending on the crystal plane. This quantum behavior persisted across distances of one micrometer and could extend tens of micrometers - plenty of room for modern electronic, photonic, and quantum devices.

"This is a fundamental observation that enables us to think about thermal management in a new way," said Hu, who is also a member of the California NanoSystems Institute at UCLA. "By enabling heat to be guided, focused and redistributed with nanoscale precision at room temperature, the discovery establishes a foundation for quantum thermal engineering." Because apparently, we now have quantum thermal engineering, and it's about to become a thing.

The ability to control heat at the atomic level could help address overheating issues in AI hardware, microelectronics, aerospace systems, and other electronics - because, as anyone who has touched a laptop after a video call knows, overheating is a real buzzkill. It might also allow tuning how phonons interact with electrons, potentially advancing quantum information systems and sensing technologies.

Previous observations of phonon focusing were mostly limited to temperatures a few degrees above absolute zero, where phonons can travel long distances without scattering. At room temperature, they normally scatter more frequently and lose coherence, causing heat to spread via ordinary diffusion. But boron arsenide experiences unusually weak phonon scattering, allowing wave-based transport to survive at room temperature. The observed heat patterns closely matched theoretical calculations, confirming that phonons in the material travel unusually long distances before scattering - a key reason the wave behavior persists.

This work builds on Hu's earlier discovery of boron arsenide in 2018, and his group has since developed high-performance thermal interfaces and gallium nitride devices using boron arsenide for cooling, underscoring the material's potential for next-generation semiconductors. The study's other authors include Man Li, Huan Wu, Zihao Qin, Chuanjin Su, and Huu Duy Nguyen, all current or former graduate students in Hu's H Lab. Funding came from the U.S. Department of Energy, the National Science Foundation, the National Institute of General Medical Sciences, and a gift from Parag and Falguni Patel. Computational resources were provided by the UCLA Institute for Digital Research and Education and by Bridges 2 at the Pittsburgh Supercomputing Center.

So, next time your phone overheats, just remember: science is working on it, one quantum phonon at a time.