Interference effects in quanum Hall - superconductor hybrid devices*

I plan to discuss our group’s two recent results: realization of the quantum Hall-based SQUID in side-gated samples; and observation of the chiral Andreev edge states – hybrid electron/hole single particle modes running along the superconductor - quantum Hall interfaces.

1) We have developed graphene Josephson junctions with self-aligned side gates, which enable full control over the electrostatic potential near the sample edges. The gates allow us to tune the local electron density in a wide range, in particular inducing counterpropagating quantum Hall edge states along either side gate. The close spacing between these states allows them to efficiently couple through Andreev reflections and carry supercurrent. When both side gates are applied, superconducting channels are created on both sides of the junction, thereby realizing a gate-tunable quantum Hall-based SQUID.

2) We observe direct signatures of chiral Andreev edge states (CAES) – single particle modes running along the superconductor - quantum Hall interfaces. Semi-classically, the CAES can be interpreted as a result of multiple Andreev reflections of a single electron/hole skipping along the interface. Experimentally, we observe fluctuations of the signal propagating along the superconducting contact and interpret them in terms of interference between the CAES.