Researchers at the UCLA Samueli School of Engineering have demonstrated that heat can travel through a crystal in concentrated, ray-like paths at room temperature. The discovery challenges the conventional view that heat in solids primarily spreads through random diffusion and could provide engineers with new methods for managing thermal energy in electronic and quantum devices, tells Science Daily.
The research focuses on phonons, quantum mechanical vibrations of atoms that carry heat through materials. A phenomenon called phonon focusing allows these vibrations to travel preferentially along specific directions determined by a crystal’s structure. Previously, this behavior had mainly been observed at temperatures only a few degrees above absolute zero, limiting its practical usefulness.
Led by UCLA mechanical and aerospace engineering professor Yongjie Hu, the researchers observed phonon focusing at room temperature in boron arsenide, a semiconductor known for its exceptionally high thermal conductivity. Using a nanoscale temperature-mapping technique, the team compared heat movement in conventional materials with that in boron arsenide. Instead of spreading outward in circular patterns, heat in boron arsenide formed distinct rays aligned with the crystal structure.
Changing the crystal orientation produced predictable sixfold, eightfold, and fourfold heat-flow patterns. The researchers detected this behavior across distances of about one micrometer, with the possibility that it could extend tens of micrometers. Boron arsenide enables this unusual behavior because its phonons experience relatively weak scattering, allowing wave-like heat transport to persist at room temperature.
The findings could change thermal management in AI hardware, microelectronics, aerospace systems, photonics, and quantum technologies. Rather than simply removing heat after it spreads, engineers could potentially guide and redistribute it around temperature-sensitive components with nanoscale precision. The research also opens possibilities for controlling interactions between phonons, electrons, and other energy carriers, establishing a foundation for quantum thermal engineering.
