Composite fermion

A composite fermion is the topological bound state of an electron and an even number of quantized vortices, sometimes visually pictured as the bound state of an electron and, attached, an even number of magnetic flux quanta. Composite fermions were originally envisioned in the context of the fractional quantum Hall effect, but subsequently took on a life of their own, exhibiting many other consequences and phenomena. The concept was first theorized by Jainendra K. Jain in 1989, who co-received the Wolf Prize in Physics in 2025 for this contribution. A further treatment of composite fermions as a Chern–Simons theory was developed by Ana María López and Eduardo Fradkin, and independently by Bertrand Halperin, Nicholas Read, Patrick A. Lee.

Vortices are an example of topological defect, and also occur in other situations. Quantized vortices are found in type II superconductors, called Abrikosov vortices. Classical vortices are relevant to the Berezenskii–Kosterlitz–Thouless transition in two-dimensional XY model.