WIGNER CRYSTALLIZATION OF IONS TRAPPED IN SUPERFLUID HE-4

A brief review is given of earlier work on the crystallization of two-dimensional fluids formed from particles that interact via repulsive Coulomb forces. The two-dimensional fluid formed from ions trapped below the surface of superfluid He-4 is described, and an account is given of the recent detection of the crystallization of this fluid. The ions are driven with an rf electric field, and absorption peaks are observed at frequencies that lead to the generation of surface capillary waves with a wavevector equal to a reciprocal lattice vector of the triangular lattice formed by the ions. The potential importance of this new technique for the detection and study of Wigner crystallization is discussed.