Observation of Umklapp processes in noncrystalline materials - art. no. 012301

Inelastic X-ray scattering data have been measured in liquid lithium at 475 K as a function of momentum transfer Q(2<Q<55 nm(-1)), and at several cons tant energies transfer E in the range 15-40 meV. This data provide a direct experimental evidence that Umklapp-like processes can be identified in the dynamic structure factor of a disordered system. Generalizing a picture va lid for a crystalline material, it is possible to relate the broadening of the Umklapp peaks to the width of the principal peak in the static structur e factor of disordered materials and therefore to the topological disorder.