Excitonic Josephson effect induced by interlayer tunneling current: robust evidence for exciton condensation

TL;DR

This paper provides robust experimental evidence for exciton condensation through the excitonic Josephson effect, demonstrating control of interlayer tunneling currents and proposing new detection methods and theoretical insights.

Contribution

It confirms the excitonic Josephson effect as evidence for exciton condensation and introduces a new proposal for detecting Josephson currents via magnetic field measurements.

Findings

Control of critical tunneling currents at edges by a second current

Identification of a critical Josephson current causing coupling collapse

Proposal for detecting Josephson current through magnetic field measurement

Abstract

The Josephson effect can be regarded as a striking manifestation of exciton condensation. It has been suggested to tune the condensate phase of bilayer excitons by applying interlayer tunneling current. A poorly-understood phenomenon observed by Huang {\it et al} [Phys. Rev. Lett. $\bf 109$, 156802 (2012)] demonstrates that the critical values of the interlayer tunneling current at either edge can be controlled by passing a second interlayer tunneling current at the other edge. We successfully attribute this novel coupling to excitonic Josephson effect induced by tunneling-current generated relative phases and indicate that Huang's experiment is very robust evidence for exciton condensation. We furthermore make a new proposal: there exists a critical Josephson current beyond which Josephson coupling collapses and external currents prefer to convert into edge-state currents to meet Huang's observation at the second tunneling current above $\pm$16nA -- a sudden decoupling of two edges accompanied by a large interedge voltage. Also, we make a feasible suggestion to detect Josephson current by measuring induced magnetic field of a ring-shaped excitonic Josephson junction. This work not only solves the long-standing uncertainty regarding the identification of exciton condensation but also opens a new direction to explore exciton condensation.