Low energy excitation in liquid Sb and liquid Bi observed in inelastic x-ray scattering spectra

Abstract

The dynamic structure factor<i>S</i>(<i>Q</i>,<i>E</i>), where<i>Q</i>and<i>E</i>are momentum and energy transfer, respectively, has been measured for liquid Sb, using inelastic x-ray scattering. A modified damped harmonic oscillator model function was applied to analyse<i>S</i>(<i>Q</i>,<i>E</i>) of liquid Sb and also to that of liquid Bi by Inui<i>et al</i>(2015<i>Phys. Rev.</i>B<b>92</b>, 054206). The obtained excitation energy was in fairly good agreement with that predicted by<i>ab initio</i>molecular dynamics simulations on these liquid semi-metals. The excitation energy of the longitudinal acoustic mode in liquid Sb and liquid Bi exhibits flat-topped<i>Q</i>dependence whereas the lower excitation energy below the longitudinal acoustic excitation shows<i>Q</i>-gap behaviour. From the viscosity estimated from the<i>Q</i>-gap experimentally obtained, it is inferred that the lower energy excitation arises from the transverse acoustic excitation in the liquids.