Evidence of two viscous relaxation processes in the collective dynamics   of liquid lithium
  New inelastic X-ray scattering experiments have been performed on liquid lithium in a wide wavevector range. With respect to the previous measurements, the instrumental resolution, improved up to 1.5 meV, allows to accurately investigate the dynamical processes determining the observed shape of the the dynamic structure factor, $S(Q,\omega)$. A detailed analysis of the lineshapes shows the co-existence of relaxation processes with both a slow and a fast characteristic timescales, and therefore that pictures of the relaxation mechanisms based on a simple viscoelastic model must be abandoned. 
T. Scopigno (University of Trento - I), U. Balucani (CNR Firenze - I),   G. Ruocco (University of L'Aquila - I), F. Sette (E...