Structural and electronic properties of expanding fluid metals

It has been theoretically predicted that interacting electron gas suffers a negative compressibility when the electron density is sufficiently reduced. Dielectric anomaly is another expression of compressional instability in which the static dielectric function of electron gas changes sign from positive to negative. In a medium with a negative dielectric function, like charges can attract. Expanding fluid alkali metals are the ideal system in which such instability of electron gas can be probed via the structural response of ions. We have performed x-ray diffraction and small angle x-ray scattering measurements using synchrotron radiation for expanding fluid rubidium and cesium. On the basis of the experimental results we discuss the existence of compressional instability and dielectric anomaly in three-dimensional electron gas.