Induced superconductivity in a fractional quantum Hall edge

Topological superconductivity, realized as an intrinsic material property or as an emerging property of a hybrid structure, represents a phase of matter where topological constraints and superconductivity coexist. The exchange-statistics (braiding) of its quasiparticles is not bosonic nor fermionic but is rather non-Abelian. Due to their exchange-statistics as well as non-locality these excitations offer a promising route towards fault-tolerant quantum computation. The simplest non-Abelian anyon is the Majorana zero mode with an Ising order. However, since braiding of Ising anyons does not offer a universal quantum gate set, theoretical studies have introduced Parafermion zero modes (PZM), an array of which supports universal topological quantum computation. The primary route to synthesize PZMs involves inducing superconductivity on a fractional quantum Hall effect (FQHE) edge.

In this talk, I will introduce high-quality graphene-based van der Waals devices with narrow superconducting electrode (NbN), in which superconductivity and robust FQHE coexist. We find crossed Andreev reflection (CAR) across the superconductor separating two counterpropagating FQHE edges. Our observed CAR probability of the integer edges is insensitive to magnetic field, temperature, and filling, thereby providing evidence for spin-orbit coupling inherited from NbN enabling the pairing of the otherwise spin-polarized edges. FQHE edges notably exhibit a CAR probability higher than that of integer edges once fully developed. This FQHE CAR probability remains nonzero down to our lowest accessible temperature, suggesting superconducting pairing of fractional charges. These results provide a route to realize novel topological superconducting phases with universal braiding statistics in FQHE–superconductor hybrid devices based on graphene and NbN.

link to the talk