But electrons in two dimensions can also behave as classical particles that interact only through the mutual repulsion of their negative charges. This occurs when they are spread much farther apart and has been difficult to achieve in the lab, so researchers are still seeing new phenomena. David Rees of RIKEN, a Japanese research institute, in Wako, Japan, and his colleagues, studied this regime using electrons floating above a liquid helium surface. At low temperatures, the electrons glide rapidly far above the surface--about 11 nanometers--and barely interact with it. At temperatures somewhat below 1 Kelvin, the repulsion between electrons generates a two-dimensional solid state known as a Wigner crystal. At higher temperatures the electrons act like a liquid.
Of course, this is significantly different than when QM effects kick in, whereby we get the fractional charge/quantum hall effect. It is interesting to note that we always think that to get quantum behavior, it usually requires difficult conditions. Here, it seems that it is difficult to see classical behavior clearly when the system has such a tendency to behave quantum mechanically.
 D.G. Rees et al., PRL v.106, p.026803 (2011).