High-temperature probe of electron compressibility via asymmetric Coulomb drag

Lateral charge transport of a two-dimensional (2D) electronic system can be much influenced by feeding a current into another closely spaced 2D conductor, known as the Coulomb drag phenomenon - a powerful probe of electron-electron interactions and collective excitations. Here, we show that Coulomb drag in a deliberately asymmetric van der Waals bilayer can serve as a layer-selective probe of electronic compressibility that remains invisible to standard transport. We devise a MoS₂/graphene double layer with large disparity in effective mass and Fermi temperature between them, separated by a ~ 3 nm hexagonal boron nitride spacer, and operate in the degenerate Fermi liquid regime. The MoS₂ drag channel exhibits constant electronic compressibility and acts as a sensitive transducer of graphene's Landau-level physics at finite magnetic fields. At elevated temperatures and moderate magnetic fields, clear Shubnikov-de Haas-like behaviour in the drag signal tracks the quantum oscillation in compressibility of graphene even when its own magnetotransport remains essentially featureless under the same conditions. Our results establish asymmetric Coulomb drag as a compressibility spectroscopy for 2D systems, enabling access to quantum phenomena that may leave only weak, or even negligible, fingerprints in transport.