UCLA Engineers Observe Phonon Focusing at Room Temperature in Boron Arsenide

• In conventional materials, they observed circular, uniform heat-spreading patterns consistent with ordinary diffusion .
• In boron arsenide, they observed striking ray-like temperature patterns, confirming that heat was being guided along specific crystal directions .
• The heat-flow patterns changed predictably with crystal orientation: different crystal planes of BAs exhibited distinct sixfold, eightfold, and fourfold focusing symmetries .
• The quantum phonon behavior persisted over distances of one micrometer and potentially up to tens of micrometers — sufficient for modern electronic, photonic, and quantum devices .
• The experimental results closely matched first-principles theoretical calculations, confirming that BAs' unusually weak phonon scattering enables long-distance wave-like transport at room temperature .

Why boron arsenide is special

Boron arsenide has been a subject of intense research since 2018, when three independent groups reported that its thermal conductivity at room temperature exceeds 1,000 W/mK — more than double that of copper or silver . The UCLA team had previously synthesized defect-free BAs crystals with the highest measured thermal conductivity among semiconductors . This unusually high conductivity is a direct sign of weak phonon scattering, which is precisely what makes room-temperature phonon focusing possible.

More recent work from the University of Houston reported that high-quality BAs crystals can achieve thermal conductivity exceeding 2,100 W/mK at room temperature, potentially surpassing even diamond . Combined with the discovery of directional heat flow, boron arsenide now offers both high conductivity and controlled heat routing.

Implications for thermal management

Electronics and AI hardware — Overheating is a major bottleneck limiting performance, reliability, and scalability in microelectronics and AI hardware. By enabling heat to be guided, focused, and redistributed with nanoscale precision at room temperature, this discovery opens the possibility of "quantum thermal engineering" — designing predetermined heat routes in chips rather than relying on bulk heat sinks after heat has already spread .

For instance, hot spots on a processor could be connected to cooler regions via phonon waveguides, eliminating the need for fans or liquid cooling in some applications. This could directly impact the design of next-generation data-center AI accelerators, where thermal limits currently constrain clock speeds and transistor density.

Quantum devices — The ability to control phonon interactions with electrons and other energy carriers at the quantum level could enable advances in quantum information processing and quantum sensing technologies, where precise thermal environment control is critical . Quantum bits are extremely sensitive to temperature fluctuations, so guided heat removal at the nanoscale could improve coherence times and device reliability.

Broader applications — The discovery could also benefit thermal management in aerospace systems, photonic devices, and next-generation semiconductor packaging, where boron arsenide's high thermal conductivity can now be combined with directional heat-flow control .

The bigger picture: quantum thermal engineering

The UCLA work is part of a broader push to treat heat at the quantum level. Earlier in 2026, researchers at Rice University reported that optical phonons in cubic boron arsenide exhibit unusually long quantum coherence — because a single optical phonon cannot decay into two acoustic phonons, a phenomenon they described as "super-long-living" quantum vibrations . Separately, Hu's group at UCLA discovered a metallic material (theta-phase tantalum nitride) with the highest thermal conductivity ever measured among metals .

Together, these findings suggest a future where engineers design heat flow with the same precision they currently design electrical current flow.

Study details: Published July 23, 2026, in Nature Physics . Authors include Man Li, Huan Wu, Zihao Qin, Chuanjin Su, and Huu Duy Nguyen (current/former UCLA graduate students) alongside Yongjie Hu . The research was funded by the U.S. Department of Energy, NSF, and NIH .