Superconducting fractional quantum Hall edges via repulsive interactions

TL;DR

This paper explores how strong repulsive interactions enable superconducting proximity effects to induce gapped phases in fractional quantum Hall edges, revealing a continuous connection between weak and strong coupling regimes.

Contribution

It demonstrates that repulsive interactions can stabilize gapped phases at strong proximity coupling, and introduces a duality mapping linking weak and strong coupling regimes.

Findings

Gapped phases are stabilized by strong repulsive interactions.

A duality transformation connects weak and strong coupling regimes.

Gapped phases are continuously connected across coupling strengths.

Abstract

We study proximity coupling between a superconductor and counter-propagating gapless modes arising on the edges of Abelian fractional quantum Hall liquids with filling fraction $\nu=1/m$ (with $m$ an odd integer). This setup can be utilized to create non-Abelian parafermion zero-modes if the coupling to the superconductor opens an energy gap in the counter-propagating modes. However, when the coupling to the superconductor is weak an energy gap is opened only in the presence of sufficiently strong attractive interactions between the edge modes, which do not commonly occur in solid state experimental realizations. We therefore investigate the possibility of obtaining a gapped phase by increasing the strength of the proximity coupling to the superconductor. To this end, we use an effective wire construction model for the quantum Hall liquid and employ renormalization group methods to obtain the phase diagram of the system. Surprisingly, at strong proximity coupling we find a gapped phase which is stabilized for sufficiently strong repulsive interactions in the bulk of the quantum Hall fluids. We furthermore identify a duality transformation that maps between the weak coupling and strong coupling regimes, and use it to show that the gapped phases in both regimes are continuously connected through an intermediate proximity coupling regime.