Structural study of expanded fluid cesium

We have performed x-ray diffraction and small-angle x-ray scattering measurements for expanded fluid cesium from the triple point up to supercritical regions. The experimental results show that the nearest neighbor distance starts to decrease and the density fluctuation increases below the density around 1.3 g cm⁻³. These structural features suggest that clustering occurs in the metallic fluid accompanying spatial atomic-density fluctuations. The density range where such inhomogeneity of the atomic arrangement appears corresponds to the region where the compressibility of the interacting electron gas has been predicted to become negative, which suggests that the observed structural changes are those induced by the instability of the electron gas.