A closely spaced but electronically isolated electronic double-layer system is fascinating to study interlayer quasiparticle interactions and to reveal intriguing interlayer correlated states. Recent progresses in the development of graphene and other two-dimensional (2D) electronic systems have sparked renewed interest in the field of strong interlayer interactions and corresponding novel quantum phases. In particular, the highly tunable electronic properties of constituent 2D layers, together with the accessibility of ultra-small interlayer separation, enable the investigation of the drag effect in previously inaccessible strong-coupling regimes.

In this talk, I will present our recent work on the interlayer drag experiments in several graphene-based electronic double-layer systems, including: 1) Revealing a fingerprint feature of drag effect between massless and massive fermions in heterostructures consisting of monolayer graphene and bilayer graphene separated by hBN spacer. 2) Discovery of a new type of quantum interference effect in inter-layer Coulomb drag, with the interference pathway comprising different carrier diffusion paths across the two constituent graphene layers. 3) Demonstration of a giant and highly-tunable drag effect between graphene and superconducting LaAlO₃/SrTiO₃ heterointerface, and a brand-new Josephson-Coulomb drag mechanism is proposed to account for such effect, rooting in the interactions between the substantially enhanced dynamical quantum fluctuations of the superconducting phases in Josephson junction arrays and the normal electrons. Our findings establish a novel platform, i.e., electronic double-layer systems, to exploit novel inter-layer quantum effects, and offer unforeseen opportunities for new-principle electronic devices.