MULTIPHONON RESPONSE IN CORRUGATED 2-DIMENSIONAL SYSTEMS

The vibrational density of states associated with the in-plane dynamic s of intercalants in graphite intercalation compounds obtained from in elastic-neutron-scattering (INS) measurements shows a characteristic t wo-peak structure. Using molecular-dynamics simulations of screened Co ulomb systems on a strongly corrugated substrate we show that the high -frequency peak is due to two-phonon response, thus providing a correc t understanding of the INS experiments. The temperature and q dependen ce of the incoherent dynamic structure factor confirms our picture.