An experiment has observed quantized charge accumulation in a system exhibiting the quantum anomalous Hall effect, its authors report. The finding provides direct experimental evidence of how charge organizes into discrete units in this class of topological materials, a phenomenon predicted in theory but difficult to isolate cleanly in the laboratory.

The quantum anomalous Hall effect arises in certain magnetic materials that, without the need for a strong external magnetic field, develop edge states through which current flows without dissipation. The charge quantization associated with these states is one of the expected signatures of their topological nature, but measuring it requires precisely separating the quantized contribution from other parasitic effects present in the sample.

The team reports the observation of quantized charge accumulation in a quantum anomalous Hall system, as stated in the title of the work. The measurement relies on controlling the magnetic state of the material and detecting the charge response associated with the occupation of the topological states.

The significance of the result lies in its reinforcement of the topological description of the quantum anomalous Hall effect, and it opens the door to using these materials as a charge reference in quantum and metrological devices. The authors point to the observation of quantized charge accumulation in a quantum anomalous Hall system as the central step of their work.