Dielectric function of<i>α</i>-Sn and its temperature dependence

Abstract

The real and imaginary parts of the dielectric function of \ensuremath{\alpha}-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 ${E}_{1}$, ${E}_{1}$+${\ensuremath{\Delta}}_{1}$, ${E}_{0}^{\mathcal{'}}$, ${E}_{0}^{\mathcal{'}}$+${\ensuremath{\Delta}}_{0}^{\mathcal{'}}$, ${E}_{2}$, ${E}_{1}^{\mathcal{'}}$, ${E}_{1}^{\mathcal{'}}$+${\ensuremath{\Delta}}_{1}^{\mathcal{'}}$, 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 \ensuremath{\alpha}-Sn. Data are also presented for the \ensuremath{\beta}-Sn obtained after heating \ensuremath{\alpha}-Sn to temperatures above 70 \ifmmode^\circ\else\textdegree\fi{}C.