Plasmons in Lithium Ammonia

We report inelastic x-ray scattering measurements of the energy, line width, and dispersion of the plasmon in metallic lithium ammonia at an electron concentration of 4 x 10 sup (18) e-/cm sup 3. These are the first measurements of the plasmons in this system, which has the lowest electronic density for which a metal plasmon has been studied. We find a plasmon whose dispersion is only slightly reduced from the RPA value, and which is quite broad with an unusual momentum dependence.