A boron arsenide crystal is like a dance floor where atoms move to a shared rhythm. After a brief flash of light, that rhythm holds steady for tens of picoseconds, and a picosecond is one trillionth of a second. Phonons, the packets of lattice vibrations, decay very slowly here.
Scientists aimed X-rays at the crystal from different angles and saw two types of vibrations. Transverse ones, where atoms shift perpendicular to the direction of motion, settle down in 29.2 picoseconds. Longitudinal ones, where atoms compress and stretch along the direction of motion, take 13.9. In silicon, both processes take about 2 picoseconds, which is several times faster. And coherent vibrations at frequencies of 0.19 and 0.27 terahertz in boron arsenide do not decay at all during the entire observation time.
This slow dance of atoms explains why boron arsenide conducts heat better than almost any other crystal. If vibrations keep their rhythm for a long time, heat is transferred without extra losses. Physicists used to think that after a flash the lattice quickly reaches equilibrium, but now it is clear that in this material individual motions live much longer, and that is exactly why it is so good at removing heat.
Boron arsenide has a thermal conductivity above 1400 W/(m·K) at room temperature, comparable to diamond, but BAs is far cheaper and easier to process. The coherent oscillation frequencies of 0.19 and 0.27 THz lie in the terahertz range, which is being actively developed for 6G wireless communications.
Arthur C. Clarke's novel "The Fountains of Paradise" describes a material with exceptional thermal conductivity for a space elevator. BAs, with its record thermal conductivity and long-lived phonons, brings science fiction closer to reality.