  In a certain regime of low carrier densities and strong correlations,
electrons can crystallize into a periodic arrangement of charge known as Wigner
crystal. Such phases are particularly interesting in one dimension (1D) as they
display a variety of charge and spin ground states which may be harnessed in
quantum devices as high-fidelity transmitters of spin information. Recent
theoretical studies suggest that the strong Coulomb interactions in Mott
insulators and other flat band systems, may provide an attractive higher
temperature platform for Wigner crystallization, but due to materials and
device constraints experimental realization has proven difficult. In this work
we use scanning tunneling microscopy at liquid helium temperatures to directly
image the formation of a 1D Wigner crystal in a Mott insulator, TaS$_2$. Charge
density wave domain walls in TaS$_2$ create band bending and provide ideal
conditions of low densities and strong interactions in 1D. STM spectroscopic
maps show that once the lower Hubbard band crosses the Fermi energy, the
charges rearrange to minimize Coulomb energy, forming zigzag patterns expected
for a 1D Wigner crystal. The zigzag charge patterns show characteristic noise
signatures signifying charge or spin fluctuations induced by the tunneling
electrons, which is expected for this more fragile condensed state. The
observation of a Wigner crystal at orders of magnitude higher temperatures
enabled by the large Coulomb energy scales combined with the low density of
electrons, makes TaS$_2$ a promising system for exploiting the charge and spin
order in 1D Wigner crystals.
