Optical dielectric constant of Pb1−xSnxTe in the narrow-gap region

Abstract

The optical dielectric constant ε∞ of Pb1−x Sn x Te has been measured for Sn fractions x of 0.0, 0.24, 0.36, 0.39, and 0.40 in the temperature range 6–120 K and at 300 K. The value of ε∞ increases from 33 for PbTe at 300 K to 60 for Pb0.61Sn0.39Te at 6 K. This maximum value appears to occur at a composition and temperature close to the L‐point band inversion. However, the relative insensitivity of ε∞ to carrier concentration suggests that this increase in ε∞ near band inversion arises from motion of the bands throughout the Brillouin zone rather than from a change in L‐point ionicity, as suggested by Wemple.