FREQUENCY-DEPENDENT DIELECTRIC FUNCTION OF A ZERO-GAP SEMICONDUCTOR

The frequency-dependent dielectric function ε(ω) of an inherently zero-gap semiconductor, such as grey tin, has unusual properties at low temperatures. In undoped samples ε(ω)∼ω-12; in doped samples interband effects considerably modify the coefficient of the additional ω-2 term from its free-carrier value, the sign being reversed for p-type impurities. These properties should be observable in reflectance measurements. © 1968 The American Physical Society.