  The interplay between the Fermi sea anisotropy, electron-electron
interaction, and localization phenomena can give rise to exotic many-body
phases. An exciting example is an anisotropic two-dimensional (2D) Wigner solid
(WS), where electrons form an ordered array with an anisotropic lattice
structure. Such a state has eluded experiments up to now as its realization is
extremely demanding: First, a WS entails very low densities where the Coulomb
interaction dominates over the kinetic (Fermi) energy. Attaining such low
densities while keeping the disorder low is very challenging. Second, the
low-density requirement has to be fulfilled in a material that hosts an
anisotropic Fermi sea. Here, we report transport measurements in a clean
(low-disorder) 2D electron system with anisotropic effective mass and Fermi
sea. The data reveal that at extremely low electron densities, when the r_s
parameter, the ratio of the Coulomb to the Fermi energy, exceeds 38, the
current-voltage characteristics become strongly nonlinear at small dc biases.
Several key features of the nonlinear characteristics, including their
anisotropic voltage thresholds, are consistent with the formation of a
disordered, anisotropic WS pinned by the ubiquitous disorder potential.
