  The behavior of two-dimensional electron gas (2DEG) in extreme coupling
limits are reasonably well-understood, but our understanding of intermediate
region remains limited. Strongly interacting electrons crystalize into a solid
phase known as the Wigner crystal at very low densities, and these evolve to a
Fermi liquid at high densities. At intermediate densities, however, where the
Wigner crystal melts into a strongly correlated electron fluid that is poorly
understood partly due to a lack of microscopic probes for delicate quantum
phases. Here we report the first imaging of a disordered Wigner solid and its
quantum densification and quantum melting behavior in a bilayer MoSe2 using a
non-invasive scanning tunneling microscopy (STM) technique. We observe a Wigner
solid with nanocrystalline domains pinned by local disorder at low hole
densities. With slightly increasing electrostatic gate voltages, the holes are
added quantum mechanically during the densification of the disordered Wigner
solid. As the hole density is increased above a threshold (p ~ 5.7 * 10e12
(cm-2)), the Wigner solid is observed to melt locally and create a mixed phase
where solid and liquid regions coexist. With increasing density, the liquid
regions gradually expand and form an apparent percolation network. Local solid
domains appear to be pinned and stabilized by local disorder over a range of
densities. Our observations are consistent with a microemulsion picture of
Wigner solid quantum melting where solid and liquid domains emerge
spontaneously and solid domains are pinned by local disorder.
