Scientists at UCLA’s Samueli School of Engineering have discovered a method to direct heat flow through solid materials at room temperature, a finding that could improve thermal management in advanced electronics and quantum systems. The research, led by mechanical and aerospace engineering professor Yongjie Hu, was published in Nature Physics and focused on how phonons—atomic vibrations that transport heat—behave in crystalline materials.
The team observed phonon focusing in boron arsenide, a semiconductor with high thermal conductivity. Rather than dispersing evenly in all directions, heat in this material follows concentrated, ray-shaped paths determined by the crystal’s structure. Researchers developed a nanoscale temperature-mapping technique to visualize this behavior and found that the heat flow patterns changed predictably based on crystal orientation, producing sixfold, eightfold, and fourfold focusing patterns depending on which crystal planes were examined.
Previously, phonon focusing could only be detected at cryogenic temperatures near absolute zero, where phonons travel long distances with minimal scattering. At room temperature, phonons typically scatter frequently and lose coherence, causing heat to spread through normal diffusion. Boron arsenide’s exceptional property of experiencing unusually weak phonon scattering allows wave-based heat transport to persist at ambient temperatures. The quantum phonon behavior remained observable across distances of one micrometer and potentially extends for tens of micrometers, a range considered practical for modern electronic devices.
The ability to control heat at nanoscale precision could address thermal management challenges in artificial intelligence hardware, microelectronics, aerospace systems and other technologies where overheating limits performance and reliability. The discovery may also enable adjustment of how phonons interact with electrons and other energy carriers, potentially supporting advances in quantum information systems and sensing technologies. The experimental results aligned closely with theoretical calculations, confirming that phonons in boron arsenide travel unusually long distances before scattering, explaining the material’s capacity to maintain wave-based behavior at room temperature.
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