Two layers of a magnetic material, rotated relative to each other by fractions of a degree, like two slightly offset screens on a window. In their normal state, they don't produce anything special, but at a certain twist angle, an unexpected effect emerges.
In the twisted metal Fe3GeTe2 (a compound of iron, germanium, and tellurium), at an angle between 0.45 and 0.75 degrees, a giant topological Hall effect appears. This means that an electric current flowing through the material is deflected sideways much more strongly than usual, due to special magnetic vortices called skyrmions. These vortices resemble tiny whirlpools in the magnetic field, and they arrange themselves into an ordered lattice.
Computer simulations showed that the skyrmions form due to alternating interactions between the layers: within a plane, they act in one direction, while between layers, they act in another. This breaks local symmetry and stabilizes the vortices. The discovery makes twisted Fe3GeTe2 a convenient platform for controlling magnetic textures in spintronics — a field where information is carried not by charge but by the electron's spin.
Skyrmions are named after British physicist Tony Skyrme, who in the 1960s proposed them as a model for particles in nuclear physics. Today, they are studied in magnetic materials as candidates for ultra-dense information storage.
In science fiction, twisted layers of materials evoke the 'graphene' technologies from Neal Stephenson's novels, where nanomaterials with special twist angles yield unexpected properties.