Quantization of particle transport lies at the heart of topological physics. In Thouless pumps—dimensionally reduced versions of the integer quantum Hall effect—quantization is dictated by the integer winding of single-band Wannier states. Here, we show that repulsive interactions can drive a transition from an integer- to a fractional-quantized Thouless pump (at fixed integer filling) by stabilizing a crystal of multiband Wannier states, each with fractional winding. We numerically illustrate the concept in few-particle systems and show that a dynamical Hartree-Fock ansatz can quantitatively reproduce the pumping phase diagram.

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• Integer quantum Hall effect
• Topological phase transition
• Topological materials
• Bloch-Floquet theorem