Think of a stack of paper: when the sheets lie perfectly aligned, light passes through them uniformly. But turn one sheet by a few degrees, and the picture changes. Something similar happens with layers in certain materials: rotate them relative to each other, and their properties change — sometimes dramatically.
Spectroscopy isn't the key here, or rather, it's not the method used. The scientists built a device they call a quantum twisting microscope. It takes two layers of a material, such as graphite, and rotates one relative to the other with high precision. Then it measures how easily electric current flows between the layers. They found that at twist angles of 21.8 and 38.2 degrees, the current flows noticeably better. These angles aren't random: they correspond to a 'convenient' alignment of the atomic lattices of the two layers, like gears that only mesh in certain positions.
The device is built on a standard atomic force microscope, which is common in many labs. To it, they added a movable platform that can rotate the sample and a special needle-like probe. The probe is made from a thin wire with a drop of graphite at its tip. When the tip touches the surface of another graphite layer, an electrical contact forms, and current can be measured. By rotating the platform, the scientists change the angle between the layers and record how the current changes.
Such a device opens the door to studying many layered materials where layer rotation affects superconductivity, magnetism, and other remarkable phenomena. In the future, this could lead to new electronic devices that switch by a simple twist.
If you twist two layers of graphene to a 'magic angle' of about 1.1 degrees, they become superconductors — conducting electricity with zero loss. This effect was discovered in 2018 and sparked an entire field of research.
In Neal Stephenson's novel 'The Diamond Age,' materials are mentioned whose properties depend on the precise stacking of atomic layers — similar to what this microscope does.