Excitonic Josephson effect in double-layer graphene junctions

TL;DR

This paper proposes that double-layer graphene can host an exciton condensate and predicts observable Josephson effects in coupled systems, providing a pathway for experimental detection of excitonic superfluidity.

Contribution

It introduces the concept of excitonic Josephson effect in double-layer graphene and calculates the conditions for observing ac and dc Josephson currents.

Findings

AC Josephson current occurs with different gate potentials.

DC Josephson current appears with phase difference and identical gate potentials.

Double-layer graphene is a promising platform for exciton condensate experiments.

Abstract

We show that double-layer graphene (DLG), where an external potential induces an charge-imbalance between $n$- and $p$-type layers, is a promising candidate to realize an exciton condensate in equilibrium. To prove this phenomenon experimentally, we suggest to couple two DLG systems, separated by a thin insulating barrier, and measure the excitonic Josephson effect. For this purpose we calculate the ac and dc Josephson currents induced by tunneling excitons and show that the former only occurs when the gate potentials of the DLG systems differ, irrespective of the phase relationship of their excitonic order parameters. A dc Josephson current develops if a finite order-parameter phase difference exists between two coupled DLG systems with identical gate potentials.