Temperature dependence of the diamagnetic and dielectric susceptibility of silicon

We report high-precision measurements of the temperature dependence of the diamagnetic susceptibility, $\chi \mathrm{}\left(T\right)\mathrm{}$, and the temperature derivative of the infrared refractive index $\frac{\mathrm{dn}}{\mathrm{dT}}$ of Si. A simple Debye-Waller picture accurately predicts the low-temperature behavior of $\frac{\mathrm{dn}}{\mathrm{dT}}$. The temperature dependence of $\frac{\mathrm{dn}}{\mathrm{dT}}$ allows the prediction of the Van Vleck paramagnetic component of the valence-electron susceptibility. The precision of the measurements of $\chi \mathrm{}\left(T\right)\mathrm{}$ and $\frac{\mathrm{dn}}{\mathrm{dT}}$ is sufficiently high to reveal that our understanding of the temperature dependence of the valence-electron diamagnetic component is incomplete.