Experimental evidence for the presence of nonacoustic excitations in molten Ga

Abstract

The nature of the broad band of microscopic excitations measured in molten gallium is investigated by means of analysis of their mode eigenvectors $I(Q,\ensuremath{\omega})$. The results, derived from neutron spectroscopy experiments, show that excitations with a dominant acoustic character are confined to low energy transfers. In contrast, those appearing at higher frequencies unmistakably exhibit optical character, as evidenced by the out-of-phase relationship shown by the phase of oscillations in $I(Q,\ensuremath{\omega})$ that become significantly shifted relative to those of the static structure factor. Such effects are shown to arise from partial covalency that is already known to be present in gaseous, cluster and crystalline forms.