Josephson-Coulomb drag effect between graphene and LaAlO3/SrTiO3 interfacial superconductor

TL;DR

This paper reports a 'super' Coulomb drag effect between graphene and LaAlO3/SrTiO3 heterointerfaces, where the passive superconductor exhibits a significantly enhanced current response driven by quantum fluctuations, with potential applications in terahertz devices.

Contribution

It introduces a novel 'super' Coulomb drag mechanism between a normal conductor and a superconductor, demonstrated in graphene and oxide heterointerface devices, with implications for superconducting electronics.

Findings

Remarkable drag signal observed near LaAlO3/SrTiO3 superconducting transition

Passive-to-active current ratio can reach about 0.3 at optimal conditions

Theoretical extrapolation suggests ratio as large as 10^5 at zero temperature

Abstract

Coulomb drag refers to the phenomenon that a charge current in one electronic circuit induces a responsive current in a neighboring circuit solely through Coulomb interactions. For conventional interactions between fermionic particles such as electrons, the as-induced drag current in the passive layer is orders of magnitude weaker than the active current due to strong dielectric screening effect between the two. Here we propose a 'super' Coulomb drag effect between an active normal conductor and a passive superconductor of Josephson junction arrays, whereby the passive current can greatly exceed the active. The drag force originates from the interactions between the substantially enhanced dynamical quantum fluctuations of the superconducting phases in the passive layer and the normal electrons in the active layer. We demonstrate this effect in the devices composed of monolayer graphene and LaAlO3/SrTiO3 heterointerface, an inherently non-uniform superconductor described by Josephson junction arrays. Remarkable drag signal is observed in the superconducting transition regime of the LaAlO3/SrTiO3 interface, with its sign independent of the carrier type in the graphene layer. 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. Strikingly, the ratio ought to be as large as 10^5 at zero temperature by theoretical extrapolation. From engineering perspective, our device may work as current or voltage transformers, and the drag mechanism lays the foundation for synchronizing Josephson-junction-array-based terahertz radiators.