Exotic Particles Called Anyons Unlock New Path to Superconductivity

Add charge to most materials and electrons simply flow. But in a rare class of quantum insulators, extra charge doesn’t move electrons at all. It creates entirely different particles. That strange transformation is now central to a new theory explaining how a topological insulator can abruptly become a superconductor.

In a study published December 19 in the Proceedings of the National Academy of Sciences, MIT physicists Zhengyan Darius Shi and T. Senthil describe how fractional quantum anomalous Hall insulators evolve when doped and disordered. Their work addresses puzzling experimental results in twisted molybdenum ditelluride, where superconductivity appears suddenly next to a fragile fractional Hall state.

These insulators host anyons, quasiparticles carrying fractional electric charge that obey statistics foreign to both fermions and bosons. Unlike their cousins in traditional quantum Hall systems, anyons in these materials can move. That mobility means disorder and motion compete in ways with no conventional analogue.

Trapped Particles Become Magnetic Whirlpools

The authors focus on a lattice state at filling factor 2/3, a phase observed in moire materials. Doping injects a finite density of anyons. At low density, disorder pins them in place, forming what the team calls an anyon glass, an insulating phase with quantized Hall conductance.

As doping increases, the balance shifts. If the dominant excitations are charge 2e/3 anyons and disorder varies smoothly, the system undergoes a direct transition into a chiral superconductor. At the critical point separating these phases, longitudinal resistance shows a universal peak near h over e squared, a signature of a fundamentally new kind of transition.

“Remarkably, across the transition, localized anyons transmute into spontaneous vortices in the superconductor, creating an unconventional ‘anomalous vortex glass’ phase,” the researchers explain.

This transmutation is the conceptual centerpiece. The same objects frozen in the insulator reappear as magnetic vortices inside the superconducting state. The result is an anomalous vortex glass, a phase with zero resistance only at absolute zero and slow, glassy vortex motion at any nonzero temperature.

Disorder Determines the Outcome

The theory also explains why experiments see different outcomes depending on microscopic disorder. If disorder fluctuates on short length scales, the clean transition splits into multiple steps, with intermediate insulating phases showing quantized electrical or thermal transport. If charge e/3 anyons dominate instead, doping doesn’t lead to superconductivity at all. The system first becomes a reentrant integer quantum Hall state and only at higher doping turns into a conventional metal.

Shi and Senthil argue this framework naturally accounts for the asymmetric phase diagram reported in twisted MoTe2 near filling 2/3. Doping on one side produces superconductivity, while doping on the other yields an apparent integer Hall response, both separated from the parent state by sharp resistance peaks.

The work suggests concrete experimental tests. Measuring the charge of delocalizing anyons, probing nonlinear current-voltage behavior, or looking for memory effects where vortices leave behind trapped anyons could directly confirm the proposed mechanism. And because anyons exist only in two dimensions and possess fractional statistics, they’re far more stable than individual electrons, making them promising candidates for quantum computing applications resistant to environmental noise.

More broadly, the study reframes superconductivity not as a simple pairing instability but as an emergent consequence of mobile anyons in a disordered topological background. It shows how disorder, often treated as a nuisance, can actively reshape quantum matter into phases that would otherwise never exist.

Proceedings of the National Academy of Sciences: 10.1073/pnas.2520608122