Kavli Affiliate: Alex Zettl
| First 5 Authors: Hongyuan Li, Ziyu Xiang, Aidan P. Reddy, Trithep Devakul, Renee Sailus
| Summary:
Semiconductor moir’e superlattices provide a versatile platform to engineer
new quantum solids composed of artificial atoms on moir’e sites. Previous
studies have mostly focused on the simplest correlated quantum solid – the
Fermi-Hubbard model – where intra-atom interactions are simplified to a single
onsite repulsion energy U. These studies have revealed novel quantum phases
ranging from Mott insulators to quantum anomalous Hall insulators at a filling
of one electron per moir’e unit cell. New types of quantum solids should arise
at even higher filling factors where the multi-electron configuration of
moir’e 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 moir’e superlattices.
Moir’e 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 moir’e superlattice comprises a new crystalline
phase of electrons: the Wigner molecular crystal. We show that these Wigner
molecular crystals are highly tunable through mechanical strain, moir’e
period, and carrier charge type. Our study presents new opportunities for
exploring quantum phenomena in moir’e quantum solids composed of
multi-electron artificial atoms.
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