Figure 1: These illustrations show helium-$3$ (yellow) adsorbed on different substrates: (a) on the surface of bulk helium-$4$ represented in blue; (b) on the surface of graphite represented in gray; and (c) on a solid layer of helium-$4$ above a graphite surface. Recent experimental evidence with graphite and helium-$4$ on graphite indicate the formation of a 2D liquid phase in the adsorbed helium-$3$ near absolute zero—depicted in (d).