Silver niobium oxide, AgNbO₃, is a layered pie of silver, niobium, and oxygen atoms. At room temperature, it behaves like an ordinary dielectric, but when cooled, the atoms start to shift, and the crystal gains electric polarization, like a compass needle, but instead of pointing north, it points in the direction of the internal electric field. For a long time, it was unclear what exact structure emerges at low temperatures.

The authors of the new study ran a computational search over all possible atomic arrangements and found a phase that had been overlooked. In this phase, the crystal lattice twists into a spiral: looking along one axis, the atoms rotate either clockwise or counterclockwise. This property is called chirality, like left and right gloves, which don't match when superimposed. It turned out that the twist direction is tightly linked to the polarization direction: flip the field, and the spiral flips too.

This coupling offers a simple way to control optical properties: apply a voltage, the crystal changes its twist, and light passes through differently. No moving parts, just an electric field. Such switches can operate very fast and could be useful in optoelectronics — where light needs to be modulated for data transmission or new types of displays.

AgNbO₃ is an inorganic, lead-free material, making it safer than many modern piezoelectrics. And the ability to control chirality with an electric field is extremely rare: usually, this requires complex molecules or magnetic fields. Here, it's all done with a simple voltage, like from an ordinary battery.