Imaging Confined Interacting Electrons in 2D Van der Waals Heterostructures

2D Van der Waals Heterostructures provide a versatile platform to engineer new quantum phases of interacting electrons due to their high tunability. However, many such phases can hardly be accessed by conventional mesoscopic probe methods. In this talk, I will show that through developing novel scanning tunneling current imaging techniques, we are able to spatially resolve new quantum phases of confined interacting electrons in 2D Van der Waals Heterostructures. Two examples will be discussed. We first demonstrate the observation of Wigner molecular crystals emerging from multi-electron artificial atoms in twisted bilayer WS₂ moiré superlattices due to the dominating Coulomb interactions. Three-electron Wigner molecules, for example, are seen to exhibit a characteristic trimer pattern. We show that these Wigner molecular crystals are highly tunable through mechanical strain, moiré period, and carrier charge type. We next study the Luttinger liquid systems in bilayer WS₂ layer stacking domain walls. In a single DW, we observed 1D Wigner crystals in the incoherent Luttinger liquid regime at low electron densities, a dimerized electron crystal due to the magneto-elastic coupling at intermediate electron densities, and a weakly interacting Luttinger liquid featuring the Freidel oscillation at high electron densities. In a periodic array of DWs, a transition from 2D electron crystal to smectic liquid crystal is observed with the increased electron density.