In layers of molybdenum telluride twisted at a specific angle, electrons behave unusually: they can split into parts. This is akin to a whole pie suddenly being cut into perfectly equal slices, even though there's only one knife. In ordinary materials, the electron's charge is indivisible, but in these layers, under strong cooling, states emerge where the charge splits into three parts.
The scientists used two methods: one measures the material's luminescence, the other how the material reflects light in a magnetic field. This way, they found magnetic states at electron fillings of one, two, and three out of three possible levels. Each state exists at its own temperature: approximately 11, 3.5, and 2.4 degrees above absolute zero. The most fragile is the one where the charge splits into three parts: it exists only within a very narrow range of electric field and at the lowest temperature.
This state is not merely magnetic: its luminescence changes when a magnetic field is applied, indicating a topological nature. Topology here means that the property persists even if the material is slightly deformed, like a knot in a rope: it cannot be untied without breaking it. Calculations confirm that the found state is topologically nontrivial, meaning it cannot be smoothly transformed into an ordinary state.
Such fractional charges are a step toward understanding how electrons interact in complex materials. In the future, they could be useful for quantum computing, which requires states robust against disturbances.
A fractional charge does not mean the electron has physically split: it is a collective behavior of many electrons that appears as a particle with one-third of an electron's charge.