Dielectric Response of SmB 6 in the Millimeter Wave Range

Abstract

The low-temperature measurements of the conductivity and dielectric permittivity of single crystalline SmB6 in the microwave and submillimeter spectral range give evidence for a 19 meV energy gap in the density of states and for a narrow donor-type band lying 3 meV below the bottom of the upper conduction band. It is shown that at temperatures 8 K < T < 20 K the dc conductivity and the electrodynamic response of SmB6 in the frequency range up to the far infrared are determined by quasi-free carriers thermally excited in the conduction band; below 8 K the carriers are localized in the narrow band showing the typical signature of hopping conductivity.