Josephson–Coulomb drag effect between graphene and a LaAlO 3 /SrTiO 3 superconductor

Coulomb drag refers to the phenomenon in which a charge current in one electronic circuit induces a responsive current in a neighbouring circuit solely through Coulomb interactions. For conventional interactions between electrons, the induced drag current in the passive layer is orders of magnitude weaker than the active current due to the strong dielectric screening effect between them. Here we show a Coulomb drag effect between an active normal conductor and a passive superconductor of Josephson junction arrays, where the passive current is of the same order as the active one. The drag force originates from the interactions between the substantially enhanced dynamical quantum fluctuations of the superconducting phases in the passive layer and normal electrons in the active layer. We demonstrate this effect in devices composed of monolayer graphene and LaAlO 3 /SrTiO 3 heterointerface. The estimated passive-to-active ratio can reach about 0.3 at the optimal gate voltage and the temperature dependence follows that of the typical Josephson energy between superconducting puddles. From an engineering perspective, our device may work as a current or voltage transformer, and the drag mechanism lays the foundation for synchronizing Josephson-junction-array-based terahertz radiators.