Dynamical structure in liquid Te using inelastic x-ray scattering: from semiconductor-metal transition to metallic regime

We have carried out inelastic x-ray scattering measurements of liquid Te at SPring-8 in Japan and obtained the dynamic structure factors S(Q,W) at 500, 650 and 800 deg. C in Q-range from 1.3 to 43 nm1 and W-range from -40 to 40 meV, respectively. Collective excitation is ascertained in each S(Q,W). Dynamical velocity vQ of the excitation mode decreases with increasing temperature, which is normal but contradicts to the behaviour of the ultrasonic sound velocity vs that anomalously increases against temperature. This contradiction means that the ultrasonic anomaly is not derived from the dynamics in this Q-region and larger-size (> a few nm) structural relaxation process exists. The value of 'positive dispersion' (≡ (vQ - vs)/vs) decreases from 70% at 500 deg. C to 15% at 800 deg. C. Large positive dispersion is also observed at the nonmetal-metal transition regime in other liquids such as supercritical Hg, which imply that this is a common phenomenon concerning with nonmetal-metal transition