Demmel F, Morkel Chr
ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
Physics Department, TUM School of Natural Sciences, TU München, 85748 Garching, Germany.
J Phys Condens Matter. 2023 Jan 10;35(11). doi: 10.1088/1361-648X/acafc9.
The intensity ratio of the Rayleigh line and the Brillouin lines can be derived within hydrodynamics and is known as the Landau-Placzek (LP) ratio. This ratio is directly related to the ratio of specific heats of the fluid. Within the microscopic wave vector range, which can be probed by inelastic neutron scattering, the intensity ratio for simple liquid metals deviates distinctly from the hydrodynamic prediction of the LP-ratio. We derive the intensity ratio from experimental data of liquid rubidium, which shows an enhanced LP-ratio by a factor 8 compared to the hydrodynamic prediction. This strong deviation indicates a further relaxation process in the microscopic wave vector range beyond hydrodynamics. That relaxation process is the viscoelastic reaction of the simple liquid to density fluctuations. Taking this process into account a modified LP-ratio is able to describe the data quite well.
瑞利线与布里渊线的强度比可在流体动力学范围内推导得出，被称为朗道 - 普拉切克（LP）比。该比值与流体的比热比直接相关。在非弹性中子散射能够探测的微观波矢范围内，简单液态金属的强度比明显偏离LP比的流体动力学预测值。我们从液态铷的实验数据中推导强度比，结果表明与流体动力学预测值相比，其LP比提高了8倍。这种强烈的偏差表明在微观波矢范围内存在超出流体动力学的进一步弛豫过程。该弛豫过程是简单液体对密度涨落的粘弹性反应。考虑到这一过程，修正后的LP比能够很好地描述这些数据。
