Flat Bands in Flatlands: Quantum Transport in 2D Superconductors and Semiconductors

In a flat band system, the charge carriers’ energy-momentum relation is very weakly dispersive. The resultant large density of states and the dominance of Coulomb potential energy relative to the kinetic energy favor the formation of strongly correlated electron states, such as ferromagnetism, nematicity, and superconductivity. The advent of two-dimensional (2D) materials and their heterostructures has ushered in a new era for exploring, tuning and engineering of flat band system. Here I will present our recent works in twisted bilayer graphene, including experimental demonstration of the resolution of the paradox of slow Fermi velocity by quantum geometry, observation of correlated insulating states at fractional fillings, and tuning superconductivity with in situ modulation of Coulomb interactions. Lastly, I will present our recent works in 2D metal chalcogenide semiconductors, such as the quantum octets and even-odd effect in few-layer PdSe 2 .