Josephson effect in graphene bilayers with adjustable relative displacement

TL;DR

This paper explores how the Josephson current in a superconducting graphene bilayer varies with relative displacement, revealing signatures that distinguish between different pairing mechanisms and stacking orders.

Contribution

It demonstrates that the Josephson current's response to displacement can differentiate between intra- and interlayer superconducting pairing mechanisms in graphene bilayers.

Findings

Supercurrent response differs for intra- and interlayer pairing.

Displacement can cause supercurrent reversal in certain stacking orders.

Josephson signals reveal pairing mechanism signatures.

Abstract

The Josephson current is investigated in a superconducting graphene bilayer where pristine graphene sheets can make in-plane or out-of-plane displacements with respect to each other. The superconductivity can be of an intrinsic nature, or due to a proximity effect. The results demonstrate that the supercurrent responds qualitatively differently to relative displacement if the superconductivity is due to either intralayer or interlayer spin-singlet electron-electron pairing, thus providing a tool to distinguish between the two mechanisms. Specifically, both the AA and AB stacking orders are studied with antiferromagnetic spin alignment. For the AA stacking order with intralayer and on-site pairing no current reversal is found. In contrast, the supercurrent may switch its direction as a function of the in-plane displacement and out-of-plane interlayer coupling for the cases of AA ordering with interlayer pairing and AB ordering with either intralayer or interlayer pairing. In addition to sign reversal, the Josephson signal displays many characteristic fingerprints which derive directly from the pairing mechanism. Thus, measurements of the Josephson current as a function of the graphene bilayer displacement open up the means achieve deeper insights into the superconducting pairing mechanism.