Heat a crystal, and its atoms start to tremble more vigorously, like strings tightened or loosened. In a LaCoO3 crystal (a compound of lanthanum, cobalt, and oxygen), heating from 2 to 650 K triggers two major rearrangements: around 100 K, the magnetic state of cobalt ions changes, and around 550 K, the material transforms from an insulator into a conductor. Between these temperatures, physicists noticed unusual behavior in one of the oxygen atomic vibrations.

This vibration, with an energy of about 10 meV (millielectronvolts — a tiny packet of energy, like a barely perceptible string tremor), becomes anomalously soft. A soft vibration is like a loosened string: it trembles slower and with greater amplitude. This softening occurs only at a specific point in the crystal's "musical tuning"—at the wave vector q = (1/2, 1/2, 1/2). It's as if one particular note in a chord suddenly sounded louder and lower.

This specific "note" matches a prediction made back in 1958 by John Goodenough. He suggested that in this material, cobalt ions could arrange into an ordered pattern of two different magnetic states, like a chessboard alternating "strong" and "weak" magnets. Now, the trembling of oxygen atoms has revealed that such patterns do indeed emerge, albeit briefly, like a flicker rather than a permanent picture.

The connection between atomic trembling and magnetic rearrangements is key to understanding how the material changes its properties. When electrons rearrange, they alter the forces between atoms, and this is audible in the crystal's "music." Such research helps create materials with desired properties — for example, thermoelectrics that convert heat into electricity, or smart sensors.