Measurement of the dynamics of a two-dimensional dislocation-mediated melting

The Kosterlitz-Thouless theory of two-dimensional melting predicts the proliferation of free dislocations in the hexatic phase. We have studied a number of these free dislocations in second-stage nitric-acid-intercalated graphite by two different techniques. We have measured their distance by determining the correlation length with neutron diffraction and independently the number of dislocation cores by measuring the diffusion of the nitric-acid molecules using incoherent quasielastic neutron scattering. These two measurements lead to the same values, which shows the validity of the microscopic assumptions of the theory in terms of dislocations.