Phonon Focusing at Room Temperature Changes How Heat Moves Through Semiconductors
Researchers have observed ray-like thermal transport in boron arsenide at room temperature for the first time, revealing wavelike heat waves that persist across micrometer distances and fan into directional patterns dictated by the crystal's symmetry.
Heat normally spreads through solids like ink in water, drifting diffusively from hot zones to cool ones. In boron arsenide, a crystalline semiconductor prized for ultrahigh thermal conductivity, it does something entirely different — moving along narrow, wavelike channels dictated by the material’s internal geometry, a behavior known as phonon focusing. Researchers have now observed this ray-like thermal transport through boron arsenide at room temperature for the first time, establishing that quantum coherence in heat flow can survive well beyond cryogenic constraints.
The effect emerges from the material’s specific atomic arrangement, which channels thermal energy along discrete geometric paths rather than allowing it to scatter randomly. Depending on a crystal’s orientation within the sample, the concentrated heat beams fan out or converge into distinct sixfold, eightfold, or fourfold patterns that map cleanly onto the material’s symmetry axes. This directional channeling means thermal management components built from the same lattice could potentially route energy with minimal cross-talk between adjacent channels, rather than losing power to isotropic diffusion.
A UCLA Samueli engineering team led by Professor Yongjie Hu brought this behavior into focus using tip-enhanced Raman spectroscopy to map the nanoscale temperature distribution across a boron arsenide sample. The technique revealed that the thermal beams do not instantly dissipate at ambient conditions; instead, the heat waves persist over distances ranging from one micrometer up to tens of micrometers before scattering dominates their trajectories. High-resolution thermal mapping confirmed that this room-temperature phonon focusing remains stable and highly localized within the semiconductor lattice.
The finding carries immediate weight for high-power electronics and advanced semiconductor routing, where heat accumulation remains the primary bottleneck for performance scaling. Traditional thermal interface materials and heat spreaders rely on bulk conductivity, which treats heat as a scalar quantity that simply needs to be moved away from junctions as fast as possible. Observing coherent thermal transport at ambient temperatures suggests that component layouts could eventually be engineered to exploit directional phonon channels, turning the crystal’s symmetry axes into functional routing tracks rather than passive structural boundaries.
Quantum effects that require extreme cold to sustain have historically remained academic curiosities when translated to macroscopic thermal behavior. Demonstrating that phonon focusing can maintain its ray-like coherence across tens of micrometers in a practical semiconductor at ambient temperatures bridges that gap between theoretical solid-state physics and scalable device engineering. The boron arsenide crystal has effectively become a proof of concept: heat does not have to be managed as a chaotic diffusion process when the underlying lattice is designed to guide it.