Soft Report - Dipartimento di Fisica - Sapienza

Microscopic Dynamics in Liquid MetalsLiquid metals are an outstanding example of systemscombining great relevance in both industrialapplications and basic science. On the one hand theyfind broad technological application ranging from theproduction of industrial coatings (walls of refinerycoker, drill pipe for oil search) to medical equipments(reconstructive devices, surgical blades) or highperformance sporting goods. Most metallic materials,indeed, need to be refined in the molten state beforebeing manufactured. On the other hand liquidmetals, in particular the monoatomic ones, havebeen recognized since long to be the prototype ofsimple liquids, in the sense that they encompassmost of the physical properties of real fluids withoutthe complications which may be present in aparticular system Inelastic.Neutron Scattering played a major role since thedevelopment of neutron facilities in the sixties. Thelast ten years, however, saw the development ofthird generation radiation sources, which opened thepossibility of performing Inelastic Scattering with Xrays, thus disclosing previously unaccessible energymomentumregions. The purely coherent response ofX-rays, moreover, combined with the mixedcoherent/incoherent response typical of neutronscattering, provides enormous potentialities todisentangle aspects related to the collectivity ofmotion from the single particle dynamics.S(Q,ω) [a.u.]B280240200160120804001501209060300Na-K44/56KNaQ = 0.29 Q Max-4 -3 -2 -1 0 1 2 3 4E / E 0180150120Collecting data on a sizeable library of system, bymeans of new X-ray and Neutron experiment andexisting literature, we identified the commonfeatures of microscopic dynamics at differentwavelengths and frequencies, from a stronglycorrelated regime to the single particle domainthrough the intermediate, hard-sphere like, kineticregime.9060300In liquid alloys a similar scenario holds. In particularthe generalized hydrodynamic theory correctlydescribes for the spectral lineshapes. An additionalrelaxation process, however, related to theconcentration fluctuation, has to be accounted forbeside the usual two-step relaxation process rulingthe acoustic properties in monoatomic fluids.References[1] T. Scopigno, G. Ruocco and F. Sette, The Reviewof Modern Physics 77, 881 (2005).[2] T. Scopigno, R. Di Leonardo, L. Comez, A.Q.R.Baron, D. Fioretto and G. Ruocco, Physical ReviewLetters 94, 155301, (2005).In the last few years, we investigated the highfrequency dynamics in several simple liquids,comprising monoatomic fluids and binary mixtures.While the long wavelength regime is well understoodin terms of ordinary hydrodynamics, the atomicmotion at lengthscales comparable to the interatomicdistance is still debated.AuthorsS. Cazzato (a,b), G. Ruocco (a,b), T. Scopigno (b).(a) Dipartimento di Fisica Universita’ Roma ‘’LaSapienza’’, 00185 Roma, Italy.(b) CRS SOFT-INFM-CNR, Roma, Italy65SOFT Scientific Report 2004-06