A light switch clicks up and down, and in each position it stays put. Two layers of hexagonal boron nitride, a material made of boron and nitrogen atoms, behave in much the same way. If you place one layer on top of another and twist, they can lock into one of two positions. For the first time, scientists have shown that these positions can be switched back and forth by simple rotation, just like flicking a switch.
To test this, they made tiny pillars of boron nitride and rotated the top pillar with the tip of an atomic force microscope. This instrument feels the surface like a finger, but far more sensitively. It turned out that rotating by 60 degrees requires less force than rotating by 120 degrees. The difference is about 40%. It is as if the switch clicks easily in one direction but with difficulty in the other.
Such a switch made of two atomic layers could be useful in nanoelectromechanical devices where you need to control the electrical properties of a material. For now, this is only a laboratory experiment, but it shows how a simple twist can turn polarization on and off. The two-layer door lock already clicks; now we just need to find a use for it.
The torque required to rotate a disk of 500 nm radius is only about 10⁻¹⁸ N·m, comparable to the moment of force exerted by the weight of a single bacterium on a lever arm of one micrometer.