A sheet of paper with square grid, one with diamond grid, and one with honeycomb — three different universes for an ant. Change the sheet, and the rules of movement change. That's roughly how electrons experience the crystal lattice: geometry dictates whether they become little magnets, superconductors, or something else. In ordinary materials, the lattice is as rigid as if engraved. Here, they've learned to redraw it with an electric field.
Experimentalists took three layers of molybdenum telluride and twisted them alternately in opposite directions. The result was a moiré pattern — a large periodic ripple that acts as an artificial lattice for electrons. Then they applied a voltage across the layers, shifting the polarization and with it the shape of the electronic honeycomb. Without a field, it's a triangular grid: at low temperatures, electrons freeze into an insulator and respond differently to a magnet. In one direction, it's a ferromagnet; in the other, an antiferromagnet with 'polarons' (an electron plus a cloud of distortions around it). Apply a stronger field, and the same system becomes honeycomb-like with a flat Chern band. In such a band, electrons barely move inside, but along the edges they flow without resistance.
This is the first time that magnetism and topological states have not just been combined but switched by voltage in the same piece of matter. Previously, each property required growing a separate crystal. Now one can imagine a device where the same platform serves as either magnetic memory or a quantum conductor, just by turning a knob.
Such a 'sheet of paper' that changes its ruling on command brings us back to the ant. But now the ant doesn't just follow the rules: it chooses which rules to follow.
Moiré patterns in twisted layers can create superconductivity at temperatures once thought unattainable for ordinary materials. The same 'sandwich' of layers behaves as a magnet or a superconductor — depending only on the twist angle and voltage.
In Neal Stephenson's novel 'The Diamond Age', matter is programmable at the level of the atomic lattice. Here, we have programming of the electronic lattice by an electric field — almost like 'smart matter' from science fiction.