  Wigner crystal, as the most fundamental exemplification where the many-body
interaction forges the electrons into a solid, experiences an intriguing
quantum melting where diverse intermediate phases are predicted to emerge near
the quantum critical point. Indications of exotic Wigner orders like bubble
phase, liquid-solid phase, and anisotropic Wigner phase have been established
by optical or transport measurements. However, the direct visualization of
lattice-scale melting order, which is of paramount importance to unequivocally
uncover the melting nature, remains challenging and lacking. Noting that Wigner
crystals have been achieved in the fractionally filled moire superlattice
recently, here, via scanning tunneling microscope, we image the quantum melting
of Wigner solid realized by further varying the moire superstructure in
monolayer YbCl3/graphene heterostructure. The Wigner solid is constructed on
the two-dimensional ensemble of interfacial electron-hole pairs derived from
charge transfer. The interplay between certain moire potential and ionic
potential leads to the quantum melting of Wigner solid evidenced by the
emergence of electron-liquid characteristic, verifying the theoretical
predictions. Particularly, akin to the classical quasicrystal made of atoms, a
dodecagonal quasicrystal made of electrons, i.e., the Wigner quasicrytal, is
visualized at the quantum melting point. In stark contrast to the
incompressible Wigner solid, the Wigner quasicrytal hosts considerable
liquefied nature unraveled by the interference ripples caused by scattering. By
virtue of the two-dimensional charge transfer interface composed of monolayer
heavy electron material and graphene, our discovery not only enriches the
exploration and understanding of quantum solid-liquid melting, but also paves
the way to directly probe the quantum critical order of correlated many-body
system.
