Sound Velocity and Attenuation in the Semiconductor-Metal Transition Region of Fluid Selenium(Condensed matter: structure and mechanical and thermal properties)

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We have measured the sound velocity, v, and sound attenuation, α, in fluid selenium up to 1700℃ and 1666 bar including the semiconductor-metal (SC-M) transition region for the first time. The ultrasonic measurements were performed by an ultrasonic pulse transmission/echo method. A coherent phase-detection technique was used for a precise velocity measurement. Anomalous changes in the temperature dependence of v were observed at pressures above 294 bar. The inflections of v were closely related to the electronic properties and served as good indicators of the SC-M transition region except for the vicinity of the liquid-gas critical point, v along isochores decreases with increasing temperature in the transition region, which means an increase in density fluctuations. Moreover, in addition to the critical attenuation, we also observed an anomalous increase in a in the transition region. The increase in α, was attributed to an increase in bulk viscosity. On the basis of these results, we point out that a mesoscopic-scale inhomogeneity between semiconducting and metallic states exists in the transition region and induces slow structural relaxation.
社団法人日本物理学会の論文
2007-01-15