论文标题
关于锗中第二声音的问题：理论上的观点
On the question of second sound in germanium: A theoretical viewpoint
论文作者
论文摘要
我们重新审视了Beardo等人最近的工作。 \ cite {Beardo2021Observation}，其中声称在锗中观察第二种声音。我们回顾了对线性的声子Boltzmann传输方程（LBTE）对碰撞运算符（或等效地，完全散射矩阵）施加的要求，以观察Hardy确定的无漂移第二声音。通过执行完整散射矩阵的特征分类，我们表明，不满足最小的非零特征值必须与奇特特征向量相关的要求。此外，频率调制热源的LBTE直接解决方案不会揭示第二声音的存在。最后，在1D频域热室中（1D-FDTR）实验几何形状中，在松弛时间近似（RTA）下对BTE的数值溶液表明，单独的相位滞后不是可观察到的适当的实验性可观察到的，用于推断第二声音。最后，我们讨论了对第二种声音“吸烟枪”的需求。
We revisit the recent work from Beardo et al. \cite{beardo2021observation} wherein the observation of second sound in germanium is claimed. We review the requirements imposed on the collision operator (or equivalently, the full scattering matrix) of the linearized phonon Boltzmann transport equation (LBTE) for the observation of driftless second sound as established by Hardy. By performing an eigendecomposition of the full scattering matrix, we show that the requirement that the smallest nonzero eigenvalue must be associated with an odd eigenvector is not satisfied. Furthermore, direct solutions to the LBTE for a frequency modulated heat source do not reveal the presence of second sound. Finally, numerical solutions to the BTE under the relaxation time approximation (RTA) in the 1D frequency-domain thermoreflectance (1D-FDTR) experimental geometry demonstrate that phase lag alone is not a suitable experimental observable for inferring second sound. We conclude by discussing the need for a second sound `smoking gun'.
