Seminars Archive

Collective mode velocity in liquid metals. An overall description from electron gas dielectric response and ion plasma dynamics.

Abstract
Starting form the empiric trend of the compressibility of solids as a function of the interstitial electron density, we use a similar approach also in the case of liquid metals to study the behaviour of the high frequency density fluctuations. In particular we will address the problem of the propagation velocity of the high frequency collective modes. From the various experimental investigations of the collective modes in liquid metals, there exist the indication that the almost uniform electron gas governs the effective ion-ion interaction[1-3]. In order to derive a trend in liquid metals, an approximate procedure was applied, by assuming that an appropriate number of valence electrons contribute to an uniform electron gas where the ions are embedded. Starting from this model where the liquid metal is treated as superposition of two plasmas interacting each other, the first one being the ion plasma and the second one the electron gas, one can derive a rather complete description of the propagation of the ion density fluctuations at high frequency. In this context high frequency refers to a frequency comparable to the ion plasma frequency. According to the equation of motion for the ion density fluctuations one can obtain the velocity of the high frequency collective modes[4], which seems to be related to the density of the electron gas in a way which looks similar to what happens in crystalline solids. Here we present a procedure to determine the appropriate electron density and the results are used to make a comparison of the theoretical predictions with the experimental data. [1] L. E. Bove, F. Sacchetti, C. Petrillo, and B. Dorner, Phys. Rev. Lett. 85, 5352 (2000). [2] L. E. Bove, B. Dorner, C. Petrillo, F. Sacchetti, J.-B. Suck, Phys. Rev. B68, 024208 (2003). [3] L. E. Bove, F. Formisano, F. Sacchetti, C. Petrillo, A. Ivanov, B. Dorner, and F. Barocchi, Phys. Rev. B71, 014207 (2005). [4] N. H. March, Liquid Metals, Cambridge University Press, Cambridge (1990).