Electron-electron interactions
The textbook picture of non-interacting electrons breaks down in the presence of strong Coulomb repulsion, giving rise to collective many-body phenomena that are notoriously difficult to predict. One of our key methodological contributions has been the development of van der Waals heterostructure-based screening techniques, enabling sub-nanometer control of the dielectric environment and thus continuous, in situ tuning of the interaction strength in a quantum material, turning Coulomb screening into a quantitative experimental knob [Domaretskiy et al., Nature 2025; Barrier et al., arXiv 2412.01577].
We have also uncovered correlated phases across a broad class of systems: electronic phase separation with multiferroic-like hysteresis in rhombohedral graphene [Shi et al. Nature 2020], electrostatically tuneable van Hove singularities and continuously evolving correlated states tied to a dual-flatness condition in twisted monolayer-bilayer graphene [Xu et al. Nat. Phys 2021, Al Ezzi et al., arXiv 2604.13958], and the role of screening in setting the pairing mechanism of unconventional superconductivity in magic-angle twisted bilayer graphene [Barrier et al., arXiv 2412.01577]. Even in ostensibly simple systems, interactions reveal unexpected physics: monolayer graphene, whose ultra-relativistic band structure has been known since 2004, hosts a strongly interacting electron-hole Dirac plasma at low carrier density that produces giant magnetoresistance [Xin et al., Nature 2023]. Together, these results establish interaction tuning as a unifying experimental strategy for mapping the phase diagrams of correlated quantum materials.