Dielectric function ofα-Sn and its temperature dependence

The real and imaginary parts of the dielectric function of α-Sn in the (1.2–5.6)-eV photon-energy region have been measured at temperatures between 100 and 350 K. Numerically obtained second derivatives of these spectra show distinct structures attributed to $E_1$, $E_1$+${\Delta }_1$, $E_0^{\mathcal{’}}$, $E_0^{\mathcal{’}}$+${\Delta }_0^{\mathcal{’}}$, $E_2$, $E_1^{\mathcal{’}}$, $E_1^{\mathcal{’}}$+${\Delta }_1^{\mathcal{’}}$, and $E_3$ interband critical points. The line shapes of these structures have been fitted to standard theoretical expressions for various types of critical points. The temperature dependence of the critical-point parameters so obtained is presented. The results are compared with other available data and with theoretical calculations based on the band structure of α-Sn. Data are also presented for the β-Sn obtained after heating α-Sn to temperatures above 70 °C.