Oral: Wigner Molecular Crystals in 2D moire heterostructures

Semiconductor moiré superlattices provide a versatile platform to engineer new quantum solids composed of artificial atoms on moiré sites. Previous studies have mostly focused on the simplest correlated quantum solid – at a filling of one electron per moiré unit cell. New types of quantum solids should arise at even higher filling factors where the multi-electron configuration of moiré artificial atoms provides new degrees of freedom. Here we report the experimental observation of Wigner molecular crystals emerging from multi-electron artificial atoms in twisted bilayer WS2 moiré superlattices. Moiré artificial atoms, unlike natural atoms, can host qualitatively different electron states due to the interplay between quantized energy levels and Coulomb interactions. Using scanning tunneling microscopy (STM), we demonstrate that Wigner molecules appear in multi-electron artificial atoms when Coulomb interactions dominate. Three-electron Wigner molecules, for example, are seen to exhibit a characteristic trimer pattern. The array of Wigner molecules observed in a moiré superlattice comprises a new crystalline phase of electrons: the Wigner molecular crystal. Our study presents new opportunities for exploring quantum phenomena in moiré quantum solids composed of multi-electron artificial atoms.