低密度アルカリ金属流体の構造研究

Abstract

Liquid alkali metals in the vicinity of the triple point behave as a simple monatomic metallic liquid. However, as the volume expands under high-pressure and temperature condition, they undergo a metal-nonmetal transition around the critical density. In order to investigate the correlation between the electronic and structural properties, we have performed x-ray diffraction and small angle x-ray scattering measurements for fluid rubidium and cesium up to supercritical conditions using synchrotron radiation at SPring-8. Experimental observation indicates that with volume expansion the nearest neighbor distance starts to decrease and the density fluctuation increases even in the density range where the fluids are metallic. The electronic density where such structural inhomogeneity appears corresponds to the theoretically calculated threshold density where the compressibility of the homogeneous interacting electron gas turns to negative. This finding suggests that the observed structural changes reflect instability of the electron gas.