Heat can now travel in focused rays at room temperature, UCLA team finds

A nanoscale temperature map of a boron arsenide crystal, captured at room temperature for the first time, shows heat moving in straight, focused rays along specific crystal directions rather than the round halo that ordinary materials produce. The result comes from a UCLA Samueli team led by mechanical and aerospace engineering professor Yongjie Hu, published in Nature Physics.

Phonon focusing is the wave-like, directional flow of heat carried by phonons, the quantized lattice vibrations that move thermal energy through solids. In most materials, phonons scatter so often that heat diffuses evenly in all directions. Boron arsenide is unusual: its phonons travel long distances before scattering, which lets the wave behavior focus heat along the crystal's natural axes, an effect previously seen only at cryogenic temperatures.

The team validated the ray pattern with first-principles Boltzmann transport simulations, which reproduced the directional flow and tied it to the crystal's symmetry, per the UCLA Samueli release. A UCLA CNSI release frames the result as a way to guide heat along predetermined paths, like optical fibers guiding light, rather than removing it after it spreads.

The work is a lab demonstration, re-reported in early August 2026. How the same directional control translates into commercial chip-cooling or quantum-device layouts remains an open engineering question.