Magnetotransport studies on the metallic side of the metal-insulator transition in PbTe

The magnetotransport properties of n- and p-type PbTe with carrier concentrations ranging from 1.4×${10}^{16}$ to 1.05×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$ were studied in fields up to 20 T and temperatures between 65 mK and 12 K. The data exhibit a strong temperature and magnetic field dependence in the extreme quantum limit. The longitudinal magnetoresistance of the sample with the smallest carrier concentration shows the most pronounced temperature dependence, similar in some respects to n-type ${\mathrm{Hg}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Cd}}_{\mathrm{x}}$Te on the metallic side of the metal-insulator transition. In order to analyze the results, the Fermi energy is calculated as a function of magnetic field for the different magnetic field orientations investigated. It is shown that the range of experimental parameters accessed rules out a Wigner condensation according to the criteria given by Gerhardts. Also, the region of a magnetic-field-induced Mott transition is just approached but not observed. In contrast to other narrow-band-gap semiconductors such as ${\mathrm{Hg}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Cd}}_{\mathrm{x}}$Te and InSb, the static dielectric constant in PbTe is huge, and the free carriers originate definitively from vacancy states which form resonant levels deep within the bands. It is suggested that the observed magnetotransport phenomena are not the onset of a Mott-Anderson transition within an impurity band formed by donors, but rather due either (i) to fluctuating band edges, or (ii) a manifestation of a high-magnetic-field-induced Anderson transition driven by quantum-mechanical interferences due to scattering.