Medium-range fluctuations accompanying the metal-nonmetal transition in expanded fluid hg.

We have carried out small angle x-ray scattering experiments of expanded fluid Hg in the metal-nonmetal (M-NM) transition region around 9.0 g cm(-3). Increase of small angle scattering intensity following the Ornstein-Zernike equation is clearly observed in the M-NM transition region as well as near the liquid-vapor critical point at 5.8 g cm(-3). The short-range correlation length, R, becomes twice as large in the M-NM transition region as in the critical region. The enhancement of R in expanded fluid Hg suggests a new type of fluctuations reflecting a first-order M-NM transition.