Diffusive Motion of Alkali Atoms in Graphite: A Quasielastic Neutron Scattering Study

ABSTRACTWe have studied the diffusive motion of alkali atoms in thermodynamic equilibrium in RbC24 by quasielastic neutron scattering. The neutron spectra show Lorentzian line profiles. The widths increase with increasing temperature. In addition a ‘de Gennes’ narrowing is observed at Q=1.2 Å-1, which coincides with the first peak in the intercalant structure factor. The narrowing becomes more pronounced at higher temperatures in contrast to a normal liquid. The data can be interpreted by the motion of clusters of alkali atoms rather than by a liquid type motion. This adds a dynamical aspect to the “floating solid’ as described by Nelson and Halperin for the melting of a 2-dimensional solid.