Classical Wigner crystals move

A novel microelectronic device promises to revolutionize our understanding of the electron crystals that form when low-density electron liquids are cooled to near absolute zero. The unusual properties of many-electron systems have lead to a number of spectacular discoveries in condensed-matter physics during the last century, including superconductivity and the fractional quantum Hall effect. Both these phenomena are essentially quantum in nature and occur when the de Broglie wavelength of an individual electron is comparable to the inter-electron separation, with electron-electron interactions playing a key role in defining the state of the system. But at the opposite extreme, i.e. at the low-density limit, one would expect the electron system to behave like a classical fluid. At low temperatures, such a fluid would solidify into what is known as a Wigner crystal, as predicted by Eugene Wigner in 1934. The electrons in a Wigner solid form a periodic spatial structure so that the energy due to mutual Coulomb repulsion is reduced. Until now Wigner crystals had only been observed in two experimental systems: electrons above the surface of liquid helium, and electrons at the interface of semiconductor heterostructures. In both cases the electrons can only move in two dimensions. Now Mike Lea at Royal Holloway University of London and co-workers have produced a two-dimensional Wigner crystal in a third system - a microchannel capillary filled with liquid helium. (U.K.)