Liquid-solid transition and the fractional quantum-Hall effect

The critical Landau-level filling factor νc for the transition from Laughlin's liquid state to a Wigner crystal is determined by comparing the energies of these states. The Wigner-crystal energy is substantially improved over the Hartree-Fock result by using a variational wave function which includes particle correlations. The liquid-state energy is obtained from the Monte Carlo calculation of Levesque, Weis, and Mac-Donald. We find νc to be slightly larger than ? which is consistent with the experimental observation by Mendez and co-workers that the fractional quantum-Hall effect does not occur for ν<~1/7. The improvement in the crystal energy by correlation is essential to this agreement since without correlations, νc~1/10. In addition the crystal correlation energy explains the very low temperatures required to see the ν=1/5 liquid state.