The study’s innovation was using the natural symmetry and vibrations of atoms to control the orbital momentum of electrons. Atoms in a solid are tightly packed together in lattice-like structures, whose shape depends on the material. In some materials, like metals, the atoms are arranged in a cube pattern, stacking together symmetrically so that their mirror image superimposes perfectly.

In chiral materials, such as quartz, the atoms are arranged in a helical pattern, like the threads of a screw. The atoms stack together with a built-in twist with either a “left-” or “right-” handedness that can’t superimpose onto each other, a symmetry called chirality. Human hands are a classic example of chiral symmetry—hold them out with the palms facing up, then put one on top of the other. That’s chiral!

Now, onto chiral phonons. Individual atoms vibrate in place while staying in a fixed position. In symmetrical materials like metals, the atoms wiggle side-to-side. In chiral materials, the twisted lattice structure forces the atoms to naturally wobble in a screw-like pattern with right- or left-handedness.

Phonons are the collective vibrations that travel through a solid, like a ripple moving through its atoms. Chiral materials have chiral phonons. Imagine you’re in the pit at a rock concert when the ballad hits. Someone starts swaying, hands in the air, forcing their neighbor to sway, and so on until the wave pattern ripples through the crowd.

The fact that the atoms vibrate in a circular, chiral path means that the atoms themselves naturally have an angular momentum. The study is the first to show that the chiral phonons’ angular momentum is transferred directly to the electrons’ orbital angular momentum.